Thermal stability and flammability properties of heterophasic PP-EP/EVA/organoclay nanocomposites

A study on the thermal behavior and flammability properties of the heterophasic polypropylene-(ethylene-propylene) copolymer (PP-EP)/poly(ethylene vinyl acetate) (EVA)/montmorillonite nanocomposite is presented. Nanoclay nanocomposites were prepared using a twin screw extruder. Both the fluidity of the EVA phase and compatibility conditions between PP-EP and EVA were used in order to obtain the required nanocomposites. Therefore, no additional compatibilizer was required to achieve the clay dispersion. Products exhibited the partially exfoliated/intercalated nanoclay dispersion. Thermogravimetric analyses indicated that nanoclays retard thermal degradation depending on nanoclay concentration. The retarding process was assigned to the exfoliation and dispersion of the silicate layers which impeded heat diffusion to the macromolecules. Thermal studies, under non-isothermal crystallization, indicated the lack of influence of nanoclay on the thermal behavior. Flammability characteristics were however affected by the nanoclay layers which overall generated flame retardation both in the EVA host and in the complex nanocomposites.