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An in-depth analysis was made on the effect of polyamide repeat structure on the morphology and mechanical properties of nanocomposites based on nylon-6, nylon-11, and nylon-12. Special care was taken to make comparisons under fixed thermal and rheological conditions. Increasing the aliphatic content relative to nylon-6 results in a decrease in the extent of organoclay exfoliation as revealed by transmission electron photomicrographs. The extent of platelet separation as judged by low-angle X-ray scattering is more complicated for nylon-11 and -12 nanocomposites than those based on nylon-6 due the presence of crystalline peaks associated with the polyamide matrix. An “exfoliation index” is used to compare stiffness effects observed in the different nanocomposites due to the large difference in the modulus of nylon-6 as compared to nylon-11 and -12. Interestingly, the exfoliation efficiency parallels morphological trends in that nylon-6 exhibits higher efficiencies than the more aliphatic nylon-11 and -12 based nanocomposites. Izod impact strengths for nanocomposites based on nylon-6 are virtually insensitive to clay content for the concentrations examined, while those for nanocomposites based on nylon-11 and -12 decreases dramatically with increasing clay concentration; this behavior is believed to stem primarily from the location of the Izod ductile-to-brittle transition temperature relative to the ambient testing temperature for the three different types of nanocomposites. In addition to repeat structure investigations, a cursory examination of the effect of nylon-6 end groups was performed.
Fornes et al. (Thu,) studied this question.