Melt blending of ethylene-vinyl alcohol copolymer/clay nanocomposites: Effect of the clay type and processing conditions

Ethylene-vinyl alcohol copolymer (EVOH)/clay nanocomposites were prepared via dynamic melt blending. The effect of the processing parameters on blends containing two clay types in different amounts was examined. The blends were characterized with a Brabender plastograph and capillary rheometer, differential scanning calorimetry, dynamic mechanical thermal analysis (DMTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). XRD showed advanced EVOH intercalation within the galleries, whereas TEM images indicated exfoliation, thereby complementing the XRD data. A dilution process with EVOH and clay treatment in an ultrasonic bath before melt blending did not add to the intercalation level. Different trends were observed for the EVOHs containing two different clay treatments, one claimed to be treated for EVOH and the other for amine-cured epoxy. They reflected the differences in the amounts of the strongly interacting polymer for the two nanocomposites. Thermal analysis showed that the melting temperature, crystallization temperature, and heat of fusion of the EVOH matrix sharply decreased with both increasing clay content and processing times. Significantly higher viscosity levels were obtained for the blends in comparison with those of the neat polymer. The DMTA spectra showed higher glass-transition temperatures for the nanocomposites in comparison with those of the neat EVOH. However, at high clay loadings, the glass-transition temperature remained constant, presumably because of an adverse plasticizing effect of the low moleculared mass onium ions treating the clays. The storage modulus improved when clay treated for EVOH was used, and it deteriorated when amine-cured epoxy clay was incorporated, except for the sonicated clay. TGA results showed significant improvements in the blends' thermal stability in comparison with that of the neat EVOH, which, according to TEM, was greater for the intercalated structures rather than for exfoliated ones. (C) 2002 Wiley Periodicals, Inc.