Computational Prediction of Mechanical Properties of PA6–Graphene/Carbon Nanotube Nanocomposites

Polyamide 6 (PA6) is a popular semicrystalline thermoplastic with good strength, stiffness, mechanical damping, wear resistance, and an excellent performance-to-cost ratio. Performance of PA6 materials can be improved with the inclusion of graphene (G) and carbon nanotubes (CNT). In this study, molecular dynamics (MD) simulations with INTERFACE and reactive INTERFACE force fields (IFF and IFF-R) were used to predict the mechanical response of amorphous PA6–CNT/G nanocomposites as a function of CNT/G loading. The mechanical property predictions for both PA6–CNT and PA6–G nanocomposites were largely similar for both bulk and Young's moduli despite a significantly greater interaction per atom between G and the PA6 matrix. The simulation conditions during polymerization (such as NVT vs NPT ensemble) have a significant effect on the predicted mechanical properties; the presence of voids may not have a detrimental effect on the mechanical response if the voids are evenly distributed throughout the nanocomposite. To validate the MD predictions, PA6–CNT/G thin films were prepared and tested for Young's modulus. The predicted values of Young's modulus agree moderately well with the experimental values; discrepancies can be attributed to the factors of a thin film vs a bulk solid, agglomeration, and crystallinity.