Morphological interpretations and micromechanical properties of polyamide-6/polypropylene-grafted-maleic anhydride/nanoclay ternary nanocomposites

Ternary nanocomposites were fabricated based on an optimized impact modified polyamide-6 (PA-6)/polypropylene grafted maleic anhydride (PP-g-MA) blend composition with varied concentrations (0-6 wt.% at a step of 2 wt.%) of organoclay, Cloisite 30BTM. The morphological attributes such as state of intercalation/exfoliation/crystalline organization and fractured surface topography of the nanocomposites were characterized by transmission electron microscopy (TEM), wide angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) while the thermal characterizations were done by conducting differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The WAXD/DSC studies have revealed that the crystallinity of the nanocomposites remained unaffected. DMA revealed an increase in glass transition temperature (Tg) of the nanocomposites by ∼14-19 oC relative to the soft polypropylene (PP)-phase, by ∼7-12 oC relative to the neat matrix PA-6 and by ∼4-9 oC relative to the optimized impact toughened PA-6 matrix while simultaneously being accompanied by the appearance of a second phase Tg peak progressively at higher temperatures as a function of nanoclay content, indicating the reinforcement effects/restrictions imposed by the nanoclay layers to the polymer chain mobility. The bulk mechanical response of the nanocomposites such as tensile, flexural and impact properties were studied and its related micromechanics aspects have been investigated using composite theories such as Halpin-Tsai, Hui-Shia, Takayanagi and Pukanszky models to analyze the interfacial effects and its role on the stress transfer efficiency. SEM analysis of fractured surface indicated that the failure mode of the nanocomposites undergoes a switch-over from interfacial-effects assisted fibrillation controlled ductile deformation to nanoclay induced soft PP-phase stiffened semi-ductile response via shear-lips formation.