Viscoelastic behavior and electrical properties of flexible nanofiber filled polymer nanocomposites. Influence of processing conditions
Résumé
Two different types of high aspect ratio flexible nanofibers, cellulose nanofibrils and carbon nanotubes, were dispersed in an amorphous thermoplastic polymer matrix. The mechanical and (in the case of carbon nanotubes filled composites) electrical properties of these composites were investigated. Dynamic mechanical analysis highlighted the influence of entanglements between fibers and of fiber/fiber contact properties on the composite mechanical reinforcement in the rubbery state. In the case of cellulose filled nanocomposites a large mechanical reinforcement effect was observed. This effect was explained by the formation of a rigid nanofibril network linked by strong hydrogen bonds. The formation of this network was assumed to be governed by a percolation mechanism. Conversely, when such bonds between cellulose fibrils were prevented by the process, a lower mechanical reinforcement is observed and can be modeled by a classical mean field approach. On the other hand, both types of composites filled with carbon nanotubes (where no strong interactions are possible) highlighted the fact that entanglements are responsible for a strong increase in thermo-mechanical stability but do not influence the mechanical reinforcement. However, carbon nanotubes are good conductive objects and for such nanocomposites, electrical percolation properties were found. The influence of the process on these electrical properties was highlighted and discussed in term of modification of tubetube contact electrical properties.