Nylon 6 nanocomposites: the effect of matrix molecular weight

Organoclay nanocomposites based on three different molecular weight grades of nylon 6 were prepared by melt processing using a twin screw extruder. Mechanical properties, transmission electron microscopy, wide-angle X-ray diffraction, and rheological measurements were used to characterize the three types of composites. Tensile modulus and yield strength were found to increase with increasing concentration of clay, while elongation at break decreased. Izod impact strength was relatively independent of clay content for the higher molecular weight composites, but slightly decreased with increasing clay content for the lowest molecular weight polyamide. In general, nanocomposites based on the higher molecular weight polyamides yielded superior composite properties, having higher degrees of clay exfoliation, higher stiffness and yield strength values, and marginal loss of ductility as compared to nanocomposites based on the low molecular weight polyamide. Differences in properties between the three types of composites were attributed to differences in melt rheology. Capillary and dynamic parallel plate data revealed sizeable differences in the levels of shear stress between each nanocomposites system. A mechanism for exfoliation during melt mixing is outlined. (C) 2001 Elsevier Science Ltd. All rights reserved.