Polyamide/layered silicate nanocomposites: A correlation between fracture toughness and molecular mobility

This study correlates toughness of polyamide nanocomposites with the molecular mobility of polymer segments in the amorphous phase. Two nanocomposite systems prepared by melt-compounding of polyamide-6 with sodium montmorillonite or organophilized montmorillonite were compared. They differed in the extent of silicate dispersion. While sodium montmorillonite formed intercalated nanocomposites, the organophilization promoted full exfoliation of the silicate layers in the matrix. The different morphology was imprinted in fracture behaviour, toughness of exfoliated nanocomposites was markedly lower that that of their intercalated counterparts. To explain this difference, a solid-state NMR was used as a selective tool for providing information about nanocomposites structure and, primarily, about dynamics of polymer segments. Comparison of NMR spin-relaxation behavior with fracture mechanics experiments revealed a close correlation between fracture toughness and the intensity of rapidly relaxing component of the amorphous phase.