Effect of -COOH functionalized carbon nanotubes on mechanical, dynamic mechanical and thermal properties of polypropylene nanocomposites

Multi-walled carbon nanotubes (CNTs) were functionalized on treatment with nitric acid and the surface-modified CNT was characterized using Fourier transform infrared spectroscopy (FTIR). Isotactic polypropylene (iPP)/CNT composites at different CNT loadings (i.e., 0.1, 0.25, 1.00, and 5.00 wt%) were prepared by melt blending in a mini blender. The differential scanning calorimetric (DSC) studies showed the nucleating effect of CNTs on the crystallization behavior of iPP. Results of X-ray diffraction studies are in conformity with the results of DSC studies. Results of stress-strain measurements reveal that Young's modulus increases, while elongation at break decreases with increase in CNT loading and the ductility of the composites is adversely affected at high loading of CNTs (>1.0 wt%). Functionalization of CNTs causes an improvement in Young's modulus, at all loadings studied, but elongation at break increases only up to 0.25%. At higher loading, the elongation at break drops down. Storage modulus increases with increase in CNT loading and the effect is greater in the case of functionalized CNTs. Tan δ shows a decrease with increase in CNT loading, but the effect is less pronounced at high CNT loading (>0.1 wt%).