Fabrication and characterization of polyamide 6-functionalized graphene nanocomposite fiber

Graphene oxide was prepared by the Hummers' method and then functionalized with 4-substituted benzoic acid via "direct Friedel-Crafts" acylation in a mild reaction medium of polyphosphoric acid/phosphorous pentoxide (P2O5). Raman spectroscopy, differential scanning calorimetry, thermo-gravimetric analysis, and transmission electron microscopy were used to characterize the resultant structure. The results show that 4-substituted benzoic acid functionalized graphene (FG) sheets were achieved without pretreatment of oxidation. Polycaprolactam (PA6)-FG composites were prepared by in situ polymerization of epsilon-caprolactam in the presence of FG. Nanocomposite fiber with 0.01-0.5 wt% content of FG was prepared with a piston spinning machine and hot-roller drawing machine. A significant enhancement of mechanical properties of the PA6-FG composites' fiber is obtained at low graphene loading; that is, a 29 % improvement of tensile strength and a three times increase of Young's modulus are achieved at a graphene loading of only 0.1 wt%. The "graft-from" methodologies pave the way to prepare graphene-based nanocomposites of condensation polymers with promising performance and functionality.