EVA nanocomposites based on South African Koppies clay

Abstract

South African Koppies bentonite was organo-modified with single tail and double tail alkyl ammonium cationic surfactants with the latter intercalated both below and above the clay CEC. Corresponding poly(ethylene-co-vinylacetate) nanocomposites were prepared by twin-screw melt compounding. Transmission electron microscopy indicated the presence of mixed nano- and micron-sized clay morphologies. X-ray diffraction studies revealed that the crystallinity of the particles improved and that the d-spacing values increased on incorporating the clays in the polymer matrix. It is postulated that, rather than indicating polymer co-intercalation, this is caused by further intercalation of either excess surfactants or surfactant residues that were released by shear delamination of the clays during compounding. Improved mechanical properties were realized especially when using the clay containing the longer double tail surfactant intercalated at levels in excess of the cation exchange capacity of the clay. The nanocomposites showed improved tensile modulus and elongation at break values at the expense of a reduction in impact strength while tensile strength was about the same as for the neat polymer.