Effects of shear on melt exfoliation of clay in preparation of nylon 6/organoclay nanocomposites

The effect of shear stress on the exfoliation of organosilicate layers in the polyamide 6 (PA6) matrix was investigated using an X-Ray diffractometer (XRD). Shear stress was controlled by changing the molecular weight of PA6, mixing temperature, and rotor speed of a mini-molder. When Cloisite(R) 30 B (30 B), which favorably interacts with PA6, was used as organosilicate, silicate layers were exfoliated even at zero shear stress when annealing time was long enough. When shear stress was applied, the exfoliation of clay took place in a much shorter time compared to the statically annealed sample, and was dependent on molecular weight of matrix and mixing temperature. For poorly interacting PA6/ Cloisite(R) 25 A nanocomposites, only well ordered intercalated ones were obtained under high shear conditions. Shear stress applied during mixing thus plays a secondary role. Breaking silicate agglomerates into primary particles facilitates polymer chains to diffuse easily into the gallery of layered silicates, and thus enhances the degree of exfoliation at a given mixing condition. Thermodynamics, especially the diffusion of polymer chain into the silicate layers, plays primary roles in preparing the nanocomposites with exfoliated structure.