Thermomechanical properties of nanotubes in a thermosetting polyimide matrix: Relationship to the percolation threshold

The objective of this research is to more fully understand the structure–property relationships in multiwalled carbon nanotube (MWNT)/high performance thermosetting polymer nanocomposites. Nanocomposites containing up to 7 wt.% MWNTs and a polyimide matrix (PETI-330) were characterized after curing and these characterization results were compared against similar nanocomposites containing carbon nanofibers (CNFs). Glass transition temperature values and thermomechanical testing indicated that the physical properties of the MWNT nanocomposites followed different trends at MWNT loadings less than and greater than the percolation threshold. In contrast, the CNF nanocomposites roughly showed a single relationship between physical property changes and CNF loading at the loadings studied here, which were all less than the percolation threshold. Overall, these results highlight the challenges in improving the properties of high performance matrices and suggest that MWNT network formation reduces reinforcement efficacy and that MWNTs can interfere with free radical curing processes.