Effect of long-length carbon nanotubes on yield, ultimate, dynamic mechanical, and thermal properties of polyamide-6 composites prepared by twin-screw extrusion

The extraordinary physical properties of multiwalled carbon nanotubes (MWCNTs) are yet to be fully realised in polyamide-6 (PA6) nanocomposites, due to difficulty in dispersion of MWCNTs within PA6 matrix, owing to high toughness of PA6 and agglomerating properties of MWCNTs. In this study, MWCNTs of high aspect ratio prepared by chemical vapour deposition (CVD) method are melt-mixed with 0.1–0.5 parts-per-hundred ratios (phr) into PA6 matrix by twin-screw extrusion. The high shearing force of co-rotating twin-screws and intermixing of the components along the back-flow channel of extruder assured uniformly dispersed MWCNTs within PA6 system. A 30.2% rise in yield strength and an 82.6% rise in Young’s modulus were noticed for 0.1 phr MWCNTs/PA6 tensile specimens over neat PA6 specimens during tensile testing. A strain hardening behaviour was shown by neat PA6, which was persistent in all its composites containing MWCNTs. A distinct trend in storage and loss behaviour, as well as 14 °C and 11 °C rise in glass transition temperatures (T_g) in loss modulus and loss factor curves, respectively, were observed for 0.5 phr MWCNTs’ reinforcement in dynamic mechanical analysis (DMA), which indicated an effective PA6–MWCNTs interaction. The improvements in crystallization and melting temperatures, as well as crystallinity values in differential scanning calorimetry (DSC) indicated nucleating effects of MWCNTs towards stable crystallization of PA6 molecules. The shifting and rise in intensity peaks in XRD and Raman spectroscopy curves supported the reinforcing effect of MWCNTs within PA6 matrix. These nanocomposites are beneficial for fabricating high mechanical and thermal stability-required components in automobiles, aerospace, and biomedicals.