Microinjection molding of polypropylene/multi-walled carbon nanotube nanocomposites: The influence of process parameters

Polypropylene (PP) filled with 10 wt% multi-walled carbon nanotube (CNT) nanocomposites were prepared via masterbatch dilution and subjected to microinjection molding (IM) under various processing conditions. The molding conditions were altered by systematically changing the machine variables, such as: melt temperature, mold temperature, backpressure and injection velocity. A mold insert with a three-step decrease in thickness along the flow direction was adopted. The effect of molding parameters on the electrical conductivity and dimensional stability of as-molded microparts was evaluated using the design of experiments (DOE) method. The distribution of maximum shear rates along the flow direction was simulated via Moldflow, and the state of dispersion of CNT within the microparts was examined by scanning electron microscopy (SEM). In addition, the thermal behavior of the microparts molded from unfilled PP and PP/CNT 10 wt% nanocomposites at different sampling positions along the flow direction was studied by differential scanning calorimetry. Results showed that the crystallization process of unfilled PP taken from different regions of the microparts is temperature dependent, which was ascribed to the variations of shearing effects undergone by the polymer melt during IM, while this effect is not significant for CNT loaded systems. POLYM. ENG. SCI., 58:E226-E234, 2018. (c) 2017 Society of Plastics Engineers