Pure polyamide 6 (PA6) and polyamide 6/carbon nanotube (PA6/CNT) composite samples with 0.5 weight percent loading of pristine or functionalized CNTs were made using a solution mixing technique. Modification of nanotube surface as a result of chemical functionalization was confirmed through the presence of lattice defects as examined under high-resolution transmission electron microscope and absorption bands characteristic of carboxylic, sulfonic and amine chemical groups. Microstructural examination of the cryogenically fractured surfaces revealed qualitative information regarding CNT dispersion within PA6 matrix and interfacial strength. X-ray diffraction studies indicated formation of thermodynamically more stable α-phase crystals. Thermogravimetric analysis revealed that CNT incorporation delayed onset of thermal degradation by as much as 70 °C in case of amine-functionalized CNTs, thus increasing thermal stability of the composites. Furthermore, addition of amine-functionalized CNTs caused an increase in crystallization and melting temperatures from the respective values of 177 and 213 °C (for neat PA6) to 211 and 230 °C (for composite), respectively.

Polyamide-6-based composites with pristine or functionalized multi-walled carbon nanotubes were produced using melt extrusion technique. After chemical functionalization, defect formation and attachment of carboxylic (−COOH) or amine (−NH₂) groups on carbon nanotubes was confirmed from high-resolution transmission electron microscope and Fourier transform infra-red spectroscope studies. Carbon nanotubes incorporation promoted growth of α-form crystals with enhanced thermal stability through increase in crystallization temperature from 162 to 192℃. Dynamic mechanical thermal analysis (DMTA) indirectly pointed out to a homogeneous, uniform dispersion of nanotubes with reduction in free volume of the polymer, exhibiting a slight increase in glass transition temperature and a significant drop in coefficient of thermal expansion value. Composites containing 0.5 wt% NH₂-carbon nanotubes show increases in elastic modulus and tensile strength by ∼60 and 76%, respectively. Uniform dispersion and high interfacial strength was manifested by drop in strain to failure and lack of evidence of carbon nanotubes debonding from the matrix.