Structure-orientation-properties relationships for polypropylene nanoclay composite films

Abstract

In this study, the morphology, orientation, as well as the mechanical and barrier properties of monolayer and multilayer nanoclay filled polypropylene (PP) obtained from the film blowing process were investigated. A significant alignment of nanoclay along the flow direction was observed from scanning electron microscopy images of the cross-section of the etched monolayer and trilayer films. The orientations of PP crystallites and clay platelets as well as the extent of intercalation and exfoliation were analyzed using a wide angle X-ray diffraction. The crystalline structure formed in PP alone was such that the b-axis oriented in the normal and transverse directions (ND and TD, respectively) and the c-axis aligned in the machine direction (MD). The addition of clay changed the orientation of the b-axis to ND, enhanced the a-axis orientation in MD, and also improved the c-axis alignment along MD. Moreover, the 001 plane (normal to platelets plane) of the nanoclays lay into ND drastically. With the incorporation of the clay tactoid, the Young’s modulus was enhanced by 25—40%, the tensile strength remained almost unchanged, and the elongation at break along TD decreased by more than 70% for all the films. The permeability to oxygen and tear resistance along MD and TD were slightly reduced with the presence of nanoparticles and percentage of nanofiller studied. The haze of the nanocomposite films increased upon the presence of clay particles, except in the case of low clay contents of 1.5 and 2.5 wt%.