Mechanical and thermal response of i-pp & s-pp/mwnt nanocomposites

Abstract

Nanocomposites based in polypropylene (both syndiotactic and isotactic) and Multiwall Carbon Nanotubes (MWNTs) directly blended in the melt via micro-extrusion, were studied. Differential Scanning Calorimetry thermal tests and Essential Work of Fracture toughness were performed on these nanocomposites. The aim was to determine the role of MWNTs, on the creation of the plastic zone and crack propagation in double -cracked tensile specimens. Results have shown a non-linear relationship of almost all properties with MWNTs content. The thermal characterization was aimed at the evaluation of the crystallinity and the melting and crystallization temperatures of both iPP and sPP nanocomposites reinforced with MWNTs. In all cases, the effect of MWNT weight fraction on the above properties was extensively studied. MWNTs have been confirmed to influence the mobility of the polymer matrix resulting in shifts in the material melting temperature and matrix crystallinity. It was also found that a crack/craze bridging mechanism can be detected in polymer matrix/ MWNT nanocomposites. This mechanism was observed as a nano-crazing procedure, in fibrillated areas of the specimen expressed as nanotube-bridged micro-cracks. These results point a promising role of the nanotubes as tougheners for future nanocomposites applications.