Effects of process parameters and surface treatments of graphene nanoplatelets on the crystallinity and thermomechanical properties of polyamide 6 composite fibers

Polyamide 6 composite fibers containing various kinds of pristine graphene nanoplatelets [P-graphene nanoplatelets (GnPs): P-M5 and P-C750] as well as oxidized GnPs (acid-M5, acid-C750) were prepared via melt spinning. Both P-GnPs and acid-GnPs were used as reinforcements to enhance the thermomechanical properties of the composite fibers. GnPs were dispersed in the polymer matrix via solution mixing followed by coagulation. Composite fibers were melt-spun using a plunger-type extrusion system, followed by stretching to the maximum draw ratio using a Godet setup. The tensile and dynamic mechanical properties of the composite fibers were tested, as well as the thermal properties. The results showed considerable enhancements in the mechanical and thermal properties of the polyamide 6 fibers due to loading with 0.5–5 wt% GnP, and the composite fibers containing 1 wt% of acid-C750 exhibited an increase of up to 76% in the tensile strength compared to that of the neat polyimide 6 fibers. Dynamic mechanical analysis, differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy were carried out to investigate the effects of the crystallinity, crystallization kinetics, and interfacial bonding on the tensile properties of the polyamide 6 composite fibers.