Elaboration and characterization of novel polyamide-12-layered titanoniobates nanocomposites
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Loı¨c LE Pluarta) and Pierre-Jean Madec Laboratoire de Chimie Mole´culaire et Thio-organique, ENSICAEN, Universite´ de Caen BasseNormandie, Centre National de la Recherche Scientifique, 14050 Caen, France
Paul-Alain Jaffres Universite´ Europe´enne de Bretagne, France; and Universite´ de Brest, Centre National de la Recherche Scientifique Unite´ Mixte de Recherche 6521, CEMCA, Institut Fe´de´ratif de Recherche 148 ScInBios, 29238 Brest, France (Received 4 November 2008; accepted 10 June 2009)
This article describes the synthesis and the characterization of a polyamide-12 filled with a nanostructured organic/inorganic titanoniobate hybrid material. The pristine oxide KTiNbO5 has been successfully organomodified by N-alkyl amines via an acido-basic reaction after a cationic exchange step as shown by x-ray diffraction. Transmission electron microscope study and scanning transmission electron microscope observations have been used to describe the change of morphology of the nanofillers before and after processing; the micronic aggregates were changed into single sheets and dispersed in the polymer. Thermomechanical properties of the composites have been determined, and their analyses with structure-properties models are consistent with the exfoliation of the organomodified titanoniobates. I. INTRODUCTION
Since the pioneer works of the Toyota Central Research group (published in 19901–4) reported the improvement of physical properties of nylon 6 by clay exfoliation, a new field of research has emerged to understand and control the dispersion of inorganic fillers in polymers to form nanocomposites.5–8 By considering the incorporation of two-dimensional inorganic materials (e.g., clays) in polymers, it is observed that the poor chemical affinity of inorganic materials with polymers and the strong interaction forces that keep mineral platelets face to face prevent nanoscale dispersion of the filler. Therefore, chemical modification of these crude fillers is a prerequisite to successfully achieve the formation of nanocomposites. The usual pretreatment consists of introducing alkyl chains in the interlayer space of inorganic-layered materials. This step is generally achieved by cationic exchange with alkylammonium ions.9–12 The consequence of this intercalation is the reduction of electrostatic forces that account for the packing of inorganic layers. Hence, the insertion of the polymer into the intercalated hybrids is facilitated. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0410
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J. Mater. Res., Vol. 24, No. 11, Nov 2009
The cation exchange capacity (CEC) depends on the chemical structure of the initial inorganic filler. For instance, montmorillonite (MMT) is known to have a quasi-ideal intermediate capacity to exchange its original cationic species with alkylammonium cations.13 Other lamellar silicates (such as mica) are characterized by a much higher theoretical cationic exchange capacity and are likely to give intercalated structures with a higher density
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