Evolution of Rubbery Plateau Region above the Melting Point of Poly(ethylene-co-vinylacetate) by the Incorporation of Montmorillonite

Poly(ethylene-co-vinylacetate) (EVA) was mixed with sodium montmorillonite (MMT) at 90/10 wt. ratio. EVA was also mixed with an organophilic montmorillonite (o-MMT) prepared by replacing Na+ in MMT with trimethylstearylammonium cation. The structure and mechanical properties of the composites were studied by scanning electron microscopy (SEM), transmission electron microscopy, wide-angle X-ray diffraction, differential scanning calorimetry, and dynamic mechanical analysis. In the EVA/MMT composite, MMT particles were poorly dispersed in the order of a few µm. The composite was opaque. By contrast, in the EVA/o-MMT composite, the exfoliated silicate layers were nicely dispersed in EVA matrix. It was a transparent material. The composite showed an interesting reinforcing effect; i.e., the rubbery plateau modulus was retained even above the melting point of EVA. The rubbery modulus seems to originate from a formation of the “house-of-cards” structure of silicate layers.