Properties of polyamide 6/multiwalled carbon nanotubes composites: The influence of processing methods

The objective of this work was to elucidate the influence of shear rates on the properties of polyamide 6/multiwalled carbon nanotube (PA6/CNT) composites which was realized by adopting different types of processing methods that feature different orders of magnitude in shear rates, such as compression molding (CM, similar to 0 s(-1)), conventional injection molding (CIM, similar to 10(2) s(-1)) and microinjection molding (mu IM, similar to 10(5) s(-1)). Electrical conductivity (sigma) results indicated that the prevailing high shearing conditions in injection molding was unfavorable for the formation of intact filler network, thereby resulting in a much lower sigma than CM counterparts. Moreover, the sigma of PA6/CNT micro-parts was higher than that of CIM macroparts when the filler content was less than 5 wt%, otherwise the sigma of CIM macroparts prevailed over that of mu IM counterparts. A better filler distribution was observed when PA6/CNT composites were processed under higher shearing conditions, as corroborated by SEM. In addition, CNTs were preferentially aligned along flow direction and a higher degree of CNT orientation was expected with increasing shear rates, as confirmed by Raman spectral analysis. The tensile strength of injection molded PA6/CNT samples increased with increasing filler concentrations, and the more preferential orientation and better distribution of CNT were considered to be the contributing factors. The comparative study of the properties of PA6/CNT composites that processed using different methods was important for their practical applications in industrial sectors.