On polyamide 6-montmorillonite nanocomposites obtained by in-situ polymerization

Nanocomposites based on polyamide 6 (PA6) and montmorillonite-type (MMT) commercial clays, either unmodified or organically modified, have been prepared by in-situ polymerization of e-caprolactam (CL). The above materials have been characterized in detail by a number of experimental techniques, including transmission electron microscopy (TEM), wide angle X-ray diffraction (WAXD), infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The formation of nanostructured systems has been checked not only for the common used w-aminoacid-modified clay, but also for other types of organoclays. In general, a correlation has been found between nanoscopic swelling of the clay in molten CL, measured by X-ray diffraction, and level of clay dispersion in PA6. Specifically, with the most swellable clays, completely exfoliated nanocomposites have been obtained. However, also layered silicates modified by compatibilizers having carboxy groups, because of the active role of the latter in CL polymerization, turned out to form delaminated nanocomposites despite their low degree of swelling in CL monomer. Both molecular mass and crystallinity of the polyamide matrix have been found to be strongly influenced by the presence of specific layered silicates. In particular, some characterization techniques (WAXD, FTIR) have evidenced a close relationship between the MMT used and PA6 crystal structure. Namely, PA6 gamma form is promoted by the clay with compatibilizer bearing the carboxy group which is able to induce the polymer to be tethered on the silicate layers, thus provoking conditions of restricted mobility to occur.