EVA-layered double hydroxide (nano)composites: Mechanism of fire retardancy

Composites of ethylene-vinyl acetate copolymer with two different layered double hydroxides have been obtained by melt blending and these have been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, thermogravimetric analysis connected to mass spectroscopy and cone calorimetry. There is some small difference in dispersion between the zinc-containing and the magnesium-containing layered double hydroxides in EVA, but both these are microcomposites with good dispersion at the micrometer level and relatively poor dispersion at the nanometer level. There is a good reduction in the peak heat release rate at 10% LDH loading. In addition to chain stripping, which involves the simultaneous loss of both acetate and a hydrogen atom, forming acetic acid, and the formation of poly(ethylene-co-acetylene), side chain fragmentation of the acetate group also occurs and may be the dominant pathway of thermal degradation in the first step. The presence of the LDH causes acetone, rather than acetic acid, to be evolved in the initial step of the degradation.