Effect of processing parameters and strain rate on mechanical properties of carbon nanotube-filled polypropylene nanocomposites

The objective of this paper was to evaluate the effect of injection molding parameters, particularly melt temperature and injection pressure, and strain rate on the mechanical properties of polypropylene (PP) filled with different contents of multi-wall carbon nanotubes (MWCNTs). Tensile specimens with 1, 3 and 5 wt.% MWCNTs were manufactured using the injection molding method and mechanical properties, such as Young's modulus, the yield strength and yield strain, the stress at break and strain at break, were measured at three different strain rates. The effects of the process variables on these mechanical properties were investigated using a set of metamodeling techniques including the Taguchi method and the analysis of variance (ANOVA). The experimental results have shown that the incorporation of MWCNTs could effectively enhance the above mentioned mechanical properties of the injection molded PP/MWCNTs nanocomposites, the reinforcing effect of MWCNTs being more pronounced at higher injection pressure. The yield strength, stress at break and Young's modulus of the PP/MWCNTs nanocomposite increased with the increase of the MWCNTs content and strain rate, while an opposite trend was found in the yield strain and strain at break. The effect of crystallinity is secondary with respect to the effect of carbon nanotubes. (C) 2013 Elsevier Ltd. All rights reserved.