Effects of uniaxial elongational flow on polyamide based nanocomposites: morphology and mechanical properties at different draw ratios

Polymer-clay nanocomposites represent an interesting topic in materials research because of their promising properties which can be obtained with very low filler content. As well known, the performances improvement of these composites is realized when clay particles are accurately dispersed in the polymer matrix and intercalation between matrix macromolecules and clay lamellae exist. Many researches have been thus devoted to the problem of producing intercalated or exfoliated structures, and to verify the internal structure of the nanocomposites. In this regard, melt rheology represents an important experimental tool which allows to prove if exfoliation and intercalation have been realized [1, 2]. Many studies on shear flow rheology of polymer-clay nanocomposites are present in the literature but there are only a few reports about the extensional flow behaviour of nanocomposite melts [3, 4]. Nevertheless, extensional flows are very common in polymer processing operation, such as in the case of film or fiber extrusion. It is thus worthy of note to study extensional rheology of melt compounded polymer-clays systems and to analyze their behaviour in order to develop proper processesing conditions for the production of nanocomposite fibres or films. This work focuses on the study of uniaxial elongational flow and to its effect on morphology and performances of polymer-layered silicate nanocomposites. In particular a polyamide based nanocomposites, prepared by twin screw extrusion melt compounding, was investigated. The elongational flow characterization was realized by converging flow method and fiber spinning technique by making use of a capillary rheometer. The performances of the resulting nanocomposite fibres were also analyzed in terms of mechanical properties