Influence of nanofillers on the deformation process in layered silicate/polyamide-12 nanocomposites

Polymer nanocomposites based on a synthetic layered silicate and polyamide-12 (PA-12) are prepared by injection molding to study their morphology, and the influence of nanofiller particles on local deformation processes. One of the most striking results from morphological studies by transmission electron microscopy is that although the layered silicates, locally stacked in the PA-12 matrix, are arranged on planes parallel to the injection molding direction, the fine lamellae are oriented with their planes perpendicular to the injection molding direction owing to nucleation at the interface between layered silicate and polymer matrix. The dispersion of layered silicates and the orientation of lamellae are reflected in the complexity of the deformation mechanisms, which in turn determine the ultimate macroscopic properties. From studies of in situ deformation under the high voltage electron microscope, it is concluded that the main deformation mechanism is microvoid formation inside the stacks of layered silicates. According to the orientation of these stacks the applied energy is dissipated by splitting, opening or sliding of separate bundles in the stacks during deformation. The nanofiller particles are load-bearing because surfaces in the microvoids are connected and hinder further growth of the microvoids, thus preventing catastrophic failure. As a consequence, the stiffness/strength/toughness balance has been synergistically improved. Finally, based on the present experimental results, a molecular network in polymer nanocomposites is proposed, that leads to the desired superfunctional characteristics. (C) 2000 Elsevier Science Ltd. All rights reserved.