Formation of a complex constrained region at the graphite nanoplatelets-polyamide 12 interface

The study focuses on understanding the interfacial interactions between graphite nanoplatelets (GNP) and polyamide 12 (PA12) in GNP/PA12 nanocomposites and the influence of GNP on the glass transition and crystallization of PA12. A complex constrained phase, consisting of immobilized amorphous and transcrystalline region, of PA12 at the GNP surface was determined. Strong correlation between the tensile modulus and the glass transition temperature and the amount of constrained phase, assessed through the thermo-mechanical and crystallization behavior of the composites, was found. The presence of the transcrystalline region was confirmed by the nucleating ability of the GNP. The complex constrained phase provides a secondary reinforcing mechanism. GNP reinforces PA12 not only because it is stronger but because it significantly alters locally the physical properties of the polymer. In conclusion, a strong link between the nano-scale interfacial interactions, the physical properties of the polymer and the bulk properties of the composites is highlighted and explained.