Synergistic effect of ammonium polyphosphate and triazine-based charring agent on the flame retardancy and combustion behavior of ethylene-vinyl acetate copolymer

Triazine-based charring agent poly(4,6-dichloro-N-hydroxyethyl-1,3,5-triazin-2-amine-1,6-diaminohexane) (CNCO-HA) with ammonium polyphosphate (APP) was chosen to prepare intumescent flame retardant ethylene-vinyl acetate copolymer (EVA) composites by melting blending. The synergistic effect of APP and CNCO-HA on the flame retardancy, combustion behavior and flame retardant mechanism of EVA are investigated. The flame retardant properties from limited oxygen index (LOI) and vertical burning test (UL-94) show that the intumescent flame retardant (IFR) shows the best effect when the mass ratio of APP to CNCO-HA is 3:2; and the LOI value of EVA/IFR composite reaches maximum value 30.9% with 30% IFR loading. When the IFR loading is only 20%, the flame retardancy of EVA/IFR still passes UL-94 V-0 rating with LOI value of 28.2%. The cone calorimeter test (CCT) results reveal that IFR clearly changes the combustion behavior of EVA and forms a char layer on the surface of the composites, consequently resulting in obvious reduction of the flammability and smoke production of EVA. The thermogravimetric analysis (TGA) and thermogravimetric analyzer coupled to a mass spectrometer (TGA/MS) results indicate that IFR improves char residue and side chain fragmentation is probably the dominant mechanism of thermal degradation. The morphology observed by digital photos and SEM demonstrate that IFR promotes to form the compact intumescent char layer. The LRS and FTIR results indicate that EVA/IFR forms more connected structures containing POP and POC bonds and polyaromatic structure.