Low-defect graphene–polyamide-6 composites and modeling the filler–matrix interface

Low-defect graphene (G) was prepared via the thermal reduction of expanded graphite in a carbon monoxide environment. G exfoliated and suspended in p-xylene was compounded in polyamide-6 (PA6) with filler content ranging from 0.1 to 6%·w/w. Interactions between G and PA6 were characterized via Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Elastic modulus (E) had increased with increasing G content, and had exceeded idealized Halpin–Tsai predictions at 0.1–1.0%·w/w G content, indicating good dispersion and filler–matrix interactions. However, further analysis with a modified rule-of-mixtures (RoM) mathematical model indicate that the quality of filler–matrix interface had been suboptimal and had deteriorated drastically with increasing G content. The evaluation of interface quality is in agreement with observed changes in thermal behavior trends. The modified RoM can be applied as a useful tool toward interpreting the mechanical properties of graphene-reinforced composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48630.