Nylon-6 nanocomposites from alkylammonium-modified clay: the role of alkyl tails on exfoliation

Nylon-6-organoclay nanocomposites were prepared by melt processing via twin-screw extrusion for the purpose of comparing the effect of the number alkyl groups attached to the nitrogen of the organic modifier on the level of organoclay exfoliation. Wide-angle X-ray scattering and transmission electron microscopy techniques were employed to assess the morphology developed in each type of nanocomposite, while stress-strain diagrams were used to evaluate mechanical property performance. Nanocomposites derived from an organoclay having no alkyl tails in the quaternary cation result in an immiscible morphology, consisting primarily of unexfoliated clay particles, whereas those derived from an organoclay having one alkyl tail in the quaternary cation lead to a well-exfoliated morphology. Increasing the number of alkyl tails to two produced a mixed structure comprised of a large fraction of clay stacks intercalated with polymer as well as a fraction of dispersed clay platelets. The extent of mechanical reinforcement parallels the degree of exfoliation. Overall, the results may be explained by the competition between the effects of platelet-platelet interactions and the interaction of the polymer with the organoclay platelet.