Improvement of the mechanical and electrical properties of polyamide 6 nanocomposites by non-covalent functionalization of multi-walled carbon nanotubes

Pyrene moieties containing amide functional groups with various alkyl chain lengths (butyl, octyl, and dodecyl) were synthesized and utilized in non-covalent functionalization of the surface of multi-walled carbon nanotubes (MWNTs). The D/G ratio of the MWNTs (derived from the Raman spectra) remained unchanged upon non-covalent functionalization of the surface of MWNTs, indicating that there were no increases in the number of defect sites on the surface of the MWNTs. PA 6 (polyamide 6)/MWNT nanocomposites were prepared by the melt-compounding method for evaluation of the mechanical and electrical properties. Flexural testing confirmed the much higher flexural modulus of the PA 6/non-covalently functionalized MWNTs relative to the PA 6/pristine MWNT nanocomposites. Furthermore, the PA 6/non-covalently functionalized MWNT nanocomposites exhibited better electrical properties due to preservation of the intrinsic structure of the MWNTs as well as the uniform dispersion of the MWNTs in the PA 6 matrix, which also played a role in the enhanced mechanical properties. It could be observed that the longer alkyl chain length of the pyrene moieties led to further improvement of the sheet resistance and mechanical properties, which is attributed to the enhanced compatibility with PA 6 derived from functionalization.