Polyamide 66 fibers synergistically reinforced with functionalized graphene and multi-walled carbon nanotubes

Graphene and carbon nanotubes are promising strengthening additives for improving the mechanical properties of polymers. Graphene oxide (GO) and carboxylic multi-walled carbon nanotubes (CMWCNTs) were functionalized through a condensation reaction to graft melamine (M) on the GO and CMWCNTs and form products (M-g-GO and M-g-CMWNTs, respectively) with amino groups. Furthermore, both M-g-GO and M-g-CMWNTs were polymerized in situ with hexanediamine adipate salts to fabricate polyamide 66(PA66)/M-g-GO/M-g-CMWNT nanocomposites. They were melt-spun into fibers with various mass ratios of M-g-GO and M-g-CMWNTs. Transmission electron microscopy confirmed that one-dimensional M-g-CMWNTs could effectively suppress the stacking of individual two-dimensional M-g-GO by bridging adjacent M-g-GO sheets, resulting in a high contact area between the M-g-GO/M-g-CMWNT structures and the polyamide 66 matrix (PA66). Scanning electron microscopy of the fracture surfaces of the composite matrix showed that the M-g-GO/M-g-CMWNT hybrid nanofillers exhibited good dispersibilities and compatibilities. Additionally, the melting and crystallization behaviors of the PA66/M-g-GO/M-g-CMWNT nanocomposite fibers were characterized. The average tensile strength of the PA66/M-g-GO/M-g-CMWNT nanocomposite fibers containing M-g-GO (0.25 wt%)/M-g-CMWNTs (0.25 wt%) was 166% higher than that of pure PA66. Moreover, the tensile strength exhibited a maximum value when the mass ratio of M-g-GO to M-g-CMWNTs was 0.25/0.25. The remarkable synergistic effect between the M-g-GO and M-g-CMWNTs for improving the mechanical properties of polyamide 66 fibers was demonstrated.