Mise en forme des thermoplastiques chargés de nanotubes de carbone : application à la microinjection de Polyamide 12

Abstract : Addition of multi-walled carbon nanotubes (MWNT) into a polymer matrix of polyamide 12(PA 12), typically an electrical insulator, can make the whole system electrically conductor. Thearrangement of MWNT in conduction pathways would be the responsible for the conduction ofelectrical charges through the material. Electrical conductivity on isotropic nanocomposites may reach an asymptotic value (~10-2 S.m-1) for MWNT content above 1,2 wt% MWNT (percolation threshold). In microinjection molding, high shear rates (~104 s-1) as well as severe temperature gradient are imposed to the nanocomposite leading to specific microstructures which determine at the same time the electrical properties. In this work, we were interested in studying the evolution of MWNT microstructure inside the melt PA 12 matrix (by rheological tests coupled withdielectric properties measurements) under particular shear rates (from 0,02 to 1 s-1) and coolingrate (3 °C.min-1) conditions. Besides, a total loss of conduction pathways in the normal direction to the flow plane is revealed when measuring the electrical conductivity on the microinjected samples. Moreover, a reduction of the in-plane conductivity was observed in comparison with the isotropic samples. Previous results suggest an arrangement in the form of weakly oriented MWNT clusters which was confirmed by the wide orientation distribution determined by Raman spectroscopy. In fact, during microinjection molding, initial MWNT aggregates would be broken into disconnected smaller ones which could explain the generalized loss of electric properties and the almost isotropic microstructure revealed at the macro and micro scale.
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Sophie Versavaud. Mise en forme des thermoplastiques chargés de nanotubes de carbone : application à la microinjection de Polyamide 12. Sciences de l'ingénieur [physics]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2012. Français. ⟨NNT : 2012ENAM0039⟩. ⟨pastel-00866487⟩

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