Review of melt-processed nanocomposites based on EVOH/organoclay

EVOH nanocomposites containing organically treated clays are unique systems in which the clay is strongly attracted to EVOH, thus affecting the morphology and the resultant thermal and mechanical properties. A strong effect of the processing conditions on morphology, thermal, and mechanical properties was observed. In highly interacting systems, under dynamic mixing conditions, in addition to a fracturing process of the clay particles, an onion-like delamination process is suggested. EVA-g-MA and LLDPE-g-MA, having polargroups, were studied as compatibitizers to further induce clay intercalation and exfoliation. The compatibilizers affected both the thermal and mechanical properties of the composites at different levels. Thermal analysis showed that with increasing compatibilizer content lower crystallinity levels result, until at a certain content no crystallization has taken place. A Ny-6 (nylon-6)/EVOH blend is an interesting host matrix for incorporation of low organoclay contents. The Ny-6/EVOH blend is a unique system that tends to hydrogen bond and also to in situ chemically react during melt mixing. The addition of clay seems to interrupt the chemical reaction between the two host polymers at certain compositions, leading to lower melt blending torque levels when clay is present. A competition between Ny-6 and EVOH regarding the intercalation process takes place. However, Ny-6 seems to lead to exfoliated structures, whereas EVOH forms intercalated structures, as revealed from combined XRD and TEM experiments, owing to thermodynamic considerations and preferential localization of the clay in Ny-6. Of special interest is the increased storage modulus seen by the presence of only 1 wt % clay, which was achieved by extrusion under high shear forces, leading to a completely exfoliated Structure. (c) 2005 Wiley Periodicals, Inc.