Uniaxial tensile deformation of microinjection molded PCL/SWCNTs nanocomposites: Effect of interfacial “soft epitaxy” on the structural evolution as studied by synchrotron SAXS and WAXD techniques

In this study, the uniaxial tensile deformation of microinjection molded poly(ε-caprolactone)/single walled carbon nanotubes (PCL/SWCNTs) nanocomposites was explored by in-situ synchrotron SAXS and WAXD methods with simultaneous stress-strain curves, and the effect of interfacial “soft epitaxy” on the structural evolution of the nanocomposites was examined as a function of SWCNTs’ content by coupling with the ex-situ DSC and density measurements. The combination of SAXS and WAXD data implies that oriented nanohybrid shish-kebab (NHSK) structures that consist of rigid SWCNTs shish surrounded by “soft epitaxy” PCL lamellar crystals were formed in injection molded PCL/SWCNTs. Similar to PCL, PCL/SWCNTs nanocomposites again present the representative stress-strain behavior of semicrystalline polymers, i.e., the structural evolution upon stretching essentially follows the same melting-recrystallization mechanism, but the evolution proceeding of PCL/SWCNTs nanocomposites is obviously depressed with the incorporation and increase of SWCNTs. This should be attributed to that the “soft epitaxy” of PCL crystallized at the surfaces of rigid SWCNTs induces the formation of the more stable NHSK crystals that are difficult to be destroyed or melted upon uniaxial deformation and therefore act as the physical crosslinks to improve the mechanical properties of the PCL/SWCNTs nanocomposites. The present findings can improve the understanding of structural evolution behavior during the tensile deformation of PCL/SWCNTs nanocomposites, and especially enhance dramatically our understanding about the underlying reinforcing mechanism of the “soft epitaxy” of semicrystalline polymers at the surfaces of CNTs on the mechanical properties of polymer/CNTs nanocomposites. [Display omitted] •NHSK structure can generate in PCL/SWCNTs nanocomposites via “soft epitaxy” crystallization.•In-situ WAXD/SAXS techniques were employed to monitor the structural evolution upon uniaxial stretching.•NHSK structure has a restriction effect on the structural transformation of PCL.•Effect of “soft epitaxy” on the structural evolution of PCL is weaker than epitaxial crystallization.