Role of clay in compatibilization of immiscible high melt strength polypropylene and ethylene vinyl acetate copolymer blends

The compatibilization efficiency of organically modified layered silicates (clay) was studied for immiscible high melt strength polypropylene/ethyl vinyl acetate (EVA) blends for the first time. The size of the dispersed EVA phase in the polypropylene matrix decreased with addition of small amounts of clay (cloisite 20A) to the blend. Scanning electron micrographs (SEM) show an efficient mixing of polymers in the presence of clay. The X-ray diffraction (XRD) and transmission electron microscopy patterns demonstrate that silicate layers are well dispersed within the phases and are also present at the interphase. This results in substantial size reduction of the dispersed phase. The blends show a drastic increase in mechanical properties with the addition of clay. Differential scanning calorimetry thermo grams further help in understanding blend miscibility in the presence of clay as denoted by the change in the melting range of the components and the crystallization behavior of the components. The dynamic rheology tests reveal a emulsion-like behavior for the blend system as denoted by the presence of a curvature or kink at lower frequencies, which further increases for the system with clay particles due to decrease in size of the dispersed phase.