Comparative rheological studies of polyamide-6 and its low loaded nanocomposite based on layered silicates

We study some rheological properties for polyamide-6 (PA-6) and a low concentrated clay nanocomposite melt based on polyamide-6 and montmorillonite. Simple shear experiments, carried out for both the neat system and nanocomposite at two different temperatures, include start up shear flows, stress relaxation after cessation of steady flow and oscillatory shear. The dynamic data for the neat PA-6 matrix differ markedly from that of the nanocomposite system, even if it has very low nanofiller concentration. Thermal stability of the PA-6 matrix imposed many restrictions on rheological studies of our systems. Therefore an experimental window was established via rheological and thermal characterization of the materials, wherein the polymer matrix was confirmed to be thermally stable. The relaxation spectra for both polymer systems were determined from linear dynamic experiments using the Pade'-Laplace procedure. A rough estimation of nanocomposite volume fraction at percolation allowed us to attribute the occurrence of extra (relative to the neat polymer) Maxwell modes observed for the nanocomposite to the formation of a particulate network above the percolation threshold.