Morphology and properties of nanocomposites formed from ethylene-vinyl acetate copolymers and organoclays

A series of ethylene-vinyl acetate copolymers, EVA, containing 0-40% VA and three organoclays, M2(HT)2, M3(HT)1 and (HE)2M1T1, were melt processed to explore the relationship between the polarity of the polymer matrix and the organoclay structure on the extent of exfoliation and properties of the resulting nanocomposites. The degree of exfoliation of the nanocomposites was evaluated by TEM, WAXS, and mechanical testing. Quantitative particle analyses of TEM images were made to give various averages of the clay dimensions and aspect ratio. The results from different techniques were generally consistent with each other. These EVA copolymer nanocomposites show dramatically improved exfoliation of the organoclay as the VA content is increased. Nanocomposites based on the organoclay with two alkyl tails always gave better exfoliation than those based on the organoclays with a single tail at all VA levels; however, the relative advantage of the two tails versus one tail seems to diminish with increased VA level. The predictions of tensile modulus using a simple composite model based on Halpin-Tsai equations show rather good agreement with the experimental data.