Clay-reinforced polyamide: Preferential orientation of the montmorillonite sheets and the polyamide crystalline lamellae

Intercalated and exfoliated nanocomposites were prepared by the extrusion and injection of polyamide-6 and highly swollen or slightly swollen montmorillonite, respectively. The microstructure of pure compounds was characterized. The basal spacing was more homogeneous in swollen montmorillonite than in nontreated montmorillonite. This was attributed to the presence of a surfactant. Surfactant crystallites were observed in swollen montmorillonite and in the nanocomposites. Their distribution is discussed. The nanocomposites exhibited anisotropic properties attributed to the orientation of the montmorillonite sheets. The preferential orientation of the montmorillonite sheets was studied in detail by small-angle X-ray scattering (SAXS). it was found to be related to the injection direction. An average distance between two sheets was also measured from the SAXS spectra. The crystallographic state of the polyamide matrix was then analyzed. The orientation of the polymer lamellac relative to the montmorillonite sheets is discussed. The orientation of the montmorillonite sheets and the polyamide lamellae is expected to play a major role in the mechanical properties of nanocomposites. (C) 2001 John Wiley & Sons, Inc.