Improving flame retardant and smoke suppression function of ethylene vinyl acetate by combining the piperazine pyrophosphate, expandable graphite and melamine phosphate.

[Display omitted] • The synergistic effect in the flame retardant system improves the fire safety of materials. • The release of toxic fumes limits the application of EVA materials. • The melt produced by piperazine pyrophosphate can effectively inhibit the "popcorn effect" of expandable graphite. Ethylene vinyl acetate copolymer combined with the expandable graphite (EG), pyrophosphate piperazine (PAPP) and melamine polyphosphate (MPP) was adopted to prepare the flame retardant EVA (FREVA) composites by melt blending. The research results showed that the PAPP/EG/MPP mixture with a mass ratio of 2:2:1 presented the optimal flame retardant effect. With the 25 wt% additive amount, EVA composites passed UL-94 V-0 level (1.6 mm), and the limiting oxygen index (LOI) reached 35.2 %. The peak of heat release rate (PHRR), total heat release (THR) and total smoke release decreased by 67.6 %, 60.9 % and 67.4 %, respectively. The Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectra (XPS), scanning electron microscope (SEM), and thermal gravimetric analyzer (TGA) were used to research the synergistic effect flame retardant mechanism of PAPP, EG and MPP in combination with the FTIR spectrometer (TG-FTIR) and the cone calorimeter test (CCT). The polyphosphoric acid non-volatile substances generated by PAPP, attached to the surface of the EG carbon layer, effectively restrained the "popcorn effect", and the char layer presented a compact and stable structure. [ABSTRACT FROM AUTHOR]