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 ele ctron 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 bet ween layered silicate and polymer matrix. The dispersion of layered silicat es and the orientation of lamellae are reflected in the complexity of the d eformation mechanisms, which in turn determine the ultimate macroscopic pro perties. From studies of in situ deformation under the high voltage electro n microscope, it is concluded that the main deformation mechanism is microv oid formation inside the stacks of layered silicates. According to the orie ntation of these stacks the applied energy is dissipated by splitting, open ing or sliding of separate bundles in the stacks during deformation. The na nofiller particles are load-bearing because surfaces in the microvoids are connected and hinder further growth of the microvoids, thus preventing cata strophic failure. As a consequence, the stiffness/strength/toughness balanc e has been synergistically improved. Finally, based on the present experime ntal results, a molecular network in polymer nanocomposites is proposed, th at leads to the desired superfunctional characteristics. (C) 2000 Elsevier Science Ltd. All rights reserved.