Effect of uniaxial elongational flow on new copoliamide based nanocomposites

The reinforcement of polymers by adding low amount of nanoscopic layered silicates is very promising in the production of high-performances plastics. It is well known that the enhanced properties are strictly correlate with the nanoscale arrangement of the silicate layers inside the polymer matrix. In this regard, melt rheology represents a powerful tool to investigate the nanostructure in solid state and, conversely to other experimental techniques that probe a very small volume, is representative of the global bulky nanostructure. The most part of studies on rheology of polymer-clay nanocomposites concerns dynamic shear measurements, while scarce attention is paid to the effects of uniaxial elongational flow on nanostructure and properties, crucial aspect for the production of polymer nanocomposite on wide scale. In particular, in the case of film or fiber extrusion, the elongational flow is common and a better understanding of its effects on the nanostructure is important to optimize the final properties. Great industrial and scientific attention is paid to polyamide-based nanocomposites prepared by melt compounding either because polyamides are inexpensive, available and widely used either because their hydrophilic nature is the base for a good compatibility with the silicate. In this work, nanocomposite at different silicate loadings were produced by melt compounding using two polyamide matrices: a nylon 6 and a commercial copolyamide having similar molecular weights. The rheological response at high shear rates was investigated in terms of steady shear viscosity and extentional viscosity, and correlated with the state of silicate exfoliation inside the two different matrices. Nanocomposite fibers were produced by fiber spinning technique and collected at different draw ratios. The structural changes of the layered silicate and crystalline regions of the different nanocomposite fibers were investigated in response to uniaxial deformation imposed and correlated with the final tensile mechanical properties with the aim to identify the processing condition and the material composition able to lead to the highest final performances