The influence of the matrix polarity on morphology and properties of ethylene vinyl acetate copolymer-carbon nanotube nanocomposites

In this study, nanocomposites based on three commercial ethylene vinyl acetate copolymers (EVA) and purified multi-walled carbon nanotubes (MWNTs) have been prepared via direct melt blending. The influence of the matrix polarity, related here to the relative content in vinyl acetate units, on the mechanical properties has been studied, by comparing the tensile properties of the nanocomposites to those of the unfilled matrices. The relative Young's modulus of the nanocomposites is shown to slightly increase with the polarity of the matrix. Tapping mode atomic force microscopy has been used to study the state of dispersion of the MWNTs in the EVA matrices. The morphological results do not show a clear dependence between the polarity of the matrix and the dispersion state of the nanotubes: increasing the vinyl acetate content in the EVA matrix does not generate a much finer dispersion of the MWNTs. This was confirmed by the experimental determination of the relative Young's modulus compared with the theoretical predictions. The increase, with the VA content, of the relative stiffness of the resulting materials is further explained by the determination of the mean aspect ratio of the dispersed particles, as evaluated using the Halpin-Tsai model.