Materials With Improved Properties From Polymer-Ceramic Nanocomposites
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FRANK-DIETER KUCHTA', PIET J. LEMSTRA', ANDREW KELLER , LAWRENCE F. 3 BATENBURG', HARTMUT R. FISCHER "
' DUTCH POLYMER INSTITUTE, P.O. Box 513, 5600 MB Eindhoven, The Netherlands 2 H. H. Wills Physics Laboratory,University of Bristol,Bristol BS8 1 TL, United Kingdom 3 TNO-TPD MaterialsResearch & Technology, P. 0. Box 595, 5600 AN Eindhoven, The Netherlands
ABSTRACT In order to link the fundamental research field of polymer crystallization with the technical important field of composite materials polymer-layered silicate nanocomposites from polyethylene (PE) are prepared and their morphology and properties are investigated. The effect of an external confinement introduced by highly anisotropic silicate layers of organically modified clay minerals on crystal growth and nanocomposite properties has been studied. The prepared nanocomposites of organically modified clay minerals and PE exhibit not only a homogeneous distribution of individual silicate layers but also of tactoids. The isothermal crystallization rate of PE in the corresponding nanocomposite at 120 'C is increased in the composite material due to the action of the silicate layers. A significant effect on crystal phase has not been observed so far but from X-ray experiments, however the crystal size seems to be influenced. The thermal stability of the nanocomposites is significantly enhanced and the decomposition mechanism has been changed due to the presence of the layered silicates within the host polymer acting as a barrier for the diffusion of small molecules like oxygen. Due to the none permanent attachment of the polymer chains to the silicate surface the thermal-mechanical properties are only moderately enhanced at low temperature while the glass transition temperature remains unaffected.
INTRODUCTION Polymer nanocomposites with molecular dispersed layered silicates (i. e. clay minerals) are gaining increasingly interest due to their often superior properties compared with
those of the matrix material. The modification of commodity polymers with such nanoscopic reinforcing elements have various potential technological applications Depending on the interaction between the layered silicates, which are typically organically modified by replacing the charge balancing interlayer cations with, e. g., alkyl ammonium ions in order to render the silicate layers organophilic, different types of nanocomposites ranging from intercalated to exfoliated are accessible. In exfoliated nanocomposites silicate layers (I nm thickness and 100- 1000 nm in lateral dimension) are homogeneously dispersed in the continuous polymer matrix. Due to the high aspect ratios of layered silicates, materials are obtained that show improved mechanical, thermal and barrier properties without a significant loss of optical transparence, toughness or impact strength P2. The reason for the reduced permeability and the enhanced mechanical properties of the nanocomposites can be seen in: i) The changes in the crystalline character of the matrix polymer; ii) The strong interaction between
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