Filler dispersion and electrical properties of polyamide 12/MWCNT-nanocomposites produced in reactive extrusion via anionic ring-opening polymerization

The reactive extrusion of lauryl lactam to polyamide 12 (PA12) of controlled molar mass was successfully performed in a microcompounder. The maximum residual monomer content was less than 1%. The in-situ polymerization in the presence of 1–5 wt.% multiwalled carbon nanotubes (MWCNTs) was studied and the processing conditions were optimized with respect to the electrical resistivity and MWCNT dispersion. Runs which yielded in higher molar mass PA12 resulted in better dispersion of MWCNTs, whereas nanocomposites with lower molar mass PA12 had lower electrical percolation thresholds (MWCNT concentration ∼1 wt.%). A high screw speed of 200 rpm was identified to cause best dispersion and the lowest percolation threshold.Subsequently, the in-situ polymerized composites were compared with composites obtained by direct melt mixing of PA12 with MWCNTs. In comparison to the composites from commercial PA12 and MWCNTs, the dispersion of primary MWCNT agglomerates via in-situ polymerization is considerably better from which better mechanical properties may be expected. However, better dispersion did not result in a reduced electrical percolation threshold and resistivity. In summary, in-situ polymerization of lauryl lactam under the given conditions was shown to be a suitable processing route to obtain good MWCNT dispersion in PA12.