Effect of melt processing conditions on the extent of exfoliation in organoclay-based nanocomposites

Polymer layered silicate nanocomposites have been studied for nearly 50 years, but few references deal with the importance of how the organoclay was processed into the plastic of choice. Many articles focus on the importance of the chemistry used to modify the surface of the clay, usually montmorillonite, without including the role of processing. This paper demonstrates the importance of both the chemistry of the clay surface and how the clay was melt processed into the thermoplastic. Two different clay treatments were added to polyamide 6 using four different types of extruders with multiple screw designs. The mixtures of organoclay and polyamide 6 were characterized by X-ray diffraction, transmission electron microscopy, and mechanical property tests. The degree of dispersion is interpreted in terms of the residence time distribution in the extruder and the intensity of shear. A model for organoclay delamination in a polymer melt is proposed that envisions the role of both shear and time.