Roles of nanofiller structure on mechanical behavior of thermoplastic nanocomposites

The roles of nanofiller structural parameters, such as filler shape, aspect ratio and orientation, on mechanical properties of thermoplastic nanocomposites have been studied. A commercial grade nylon-6/clay nanocomposite is subjected to a large-scale simple shear orientation process and the resulting morphology is investigated on various length scale levels. Both the orientation and the aspect ratio of nanoclays, which can be altered by the simple shear process, have been studied. The incorporation of well-dispersed nanoclays into the nylon-6 matrix greatly reduces the chain mobility as well as the crystallinity of nylon-6. The exfoliated nanocomposites show that the global orientation of clay layers dictates the orientation of crystalline lamellae. Two types of lamellar orientation are observed, as revealed by small-angle X-ray scattering. One type of lamellae is oriented ∼41° away from the clay surface, whereas the simple shear process induces another weak preferred lamellar orientation nearly perpendicular to the clay surface. The formation of those lamellar orientations appears to be related to both orientation of the clay in the nanocomposite and the simple shear process. It is found that the modulus, strength, and heat distortion temperature of the nanocomposites decrease as the clay aspect ratio and degree of orientation are reduced. The micromechanics-based models accurately describe the relationship between clay structural parameters and the corresponding moduli for exfoliated nanocomposites. The impact fracture mechanisms of polypropylene (PP)-calcium carbonate (CaCO3) nanoparticles have been investigated. A detailed investigation reveals that the CaCO 3 nanoparticles act as stress concentrators to initiate massive crazes, followed by shear banding in the PP matrix.