Mechanical behaviors of polypropylene/carbon nanotube nanocomposites: The effects of loading rate and temperature

Polypropylene (PP) nanocomposites reinforced with 0.1, 0.3, 0.5 and 1.0 wt% multi-walled carbon nanotubes (MWNTs) were prepared via melt-compounding in a twin-screw extruder followed by injection molding. The effects of MWNT additions on the structure, mechanical and yielding behavior of PP were studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile tests. XRD traces showed that PP crystallized exclusively in α-form within the nanocomposite, indicating that the presence of MWNT did not influence the crystal structure of PP/MWNT nanocomposites via injection processing. DSC results confirmed that the corporation of MWNT enhanced the nucleation process on PP crystallization. It was also found that the glass transition temperature (Tg) and the activation energy (ΔE) increased with the increase of the amount of MWNT, demonstrating that the mobility of the polymer chain is reduced in the presence of MWNT. DMA analysis showed that the storage modulus and heat deflection temperature of PP/MWNT nanocomposite are improved considerably by adding only 0.3–0.5 wt% MWNT. The PP/MWNT nanocomposites were found to be strain rate and temperature dependence. Their yield stress was described successfully by Erying's equation. An index “n” was proposed to characterize the reinforcing effect of MWNTs in PP at a given temperature. The results showed that the n values for the PP/MWNT nanocomposites tend to increase with increasing test temperatures, indicating that the reinforcing effect of MWNTs in PP matrix is more pronounced at higher temperatures.