Nanostructure development in nylon 6-Cloisite® 30B composites. Effects of the preparation conditions

Abstract

PA6 composites with Cloisite® 30B (30B), prepared by different procedures, i.e., melt compounding, static annealing and solution blending, have been characterized by X-ray diffraction and microscopic analyses (TEM, SEM, POM) in order to shed more light on the mechanism of nanostructure development. It has been demonstrated that intercalation of the PA6 chains within the 30B galleries takes place very rapidly, in the absence of applied stresses, even when the size of the clay particles is relatively large (tens of microns) and the clay loading is very high (even 50 wt.%). It has also been shown that, if, conversely, the filler content is low (∼10 wt.% or less) and the particles are tiny (e.g., as for polymer/clay mixtures prepared by precipitation from a common solution), intercalation continues, under quiescent conditions, and leads in reasonable times to complete destruction of the silicate platelets stacking order. The composites with higher filler contents display a mixed exfoliated/intercalated morphology, with the intercalated silicate stacks characterized by an interlayer distance of about 3.7 nm. Contrary to statically annealed composites, the melt kneaded ones are characterized by a homogeneous dispersion of the filler particles and a local parallel orientation of the silicate platelets that induces, during polymer crystallization, an orientation of the polymer crystallites parallel to the faces of the compression molded specimens. Experiments carried out using 30B samples previously treated at 250 °C for 4 h under vacuum (30B degr) indicate that this treatment, probably due to the collapsed interlayer spaces, lowers the extent of PA6 chains intercalation. Thus, the relevant PA6/30B degr composites are characterized by the coexistence of unintercalated clay tactoids/agglomerates and individual silicate layers formed as result of intercalation on the edges of the filler particles.