Polyamide/carbonaceous particles nanocomposites fibers: Morphology and performances

In this work, the influence of carbonaceous particles with different sizes and shapes on the morphology and mechanical performances of polyamide (PA)-based fibers was investigated. Graphene nanoplatelets (GNP) are compared with spherical and rod-like carbon fillers such as carbon black (CB) and multiwall carbon nanotubes (CNTs). The increments of the complex viscosity as well as elastic and loss moduli, in the melt state, assessed by rheological analysis, are reduced by modifying polyamide (PA) matrix with nanofillers in a following order: CNTs-‰>-‰GNP-‰>-‰CB. All the nanocomposites, however, show viscosity and moduli higher than those of neat PA. The CB loading causes a mere increase of the viscosity without altering the relaxation spectrum of PA macromolecules, differently, both GNP and CNTs generate significant rheological alteration suggesting a good dispersion into PA and probable formation of semi-three-dimensional network. The increase of rigidity of the neat PA and all the three investigated nanocomposites fibers as a function of the cold draw follows the same trend observed by the rheological investigation. The morphology changes of PA achieved upon extensional flow and nanofillers adding have been investigated through transmission electron microscopy observations. Furthermore, the variation of the crystalline PA phase due to filler loading and stretching is also detected by thermal analysis and nuclear magnetic resonance analysis in the solid state. The different morphologies of the particles control and determine their dispersion and alignment in PA fibers upon elongational flow and play a key role in structure-property relationships.