Rheological and Mechanical Properties of Thermoplastic Crystallizable Polyimide-Based Nanocomposites Filled with Carbon Nanotubes: Computer Simulations and Experiments.

Recently, a strong structural ordering of thermoplastic semi-crystalline polyimides near single-walled carbon nanotubes (SWCNTs) was found that can enhance their mechanical properties. In this study, a comparative analysis of the results of microsecond-scale all-atom computer simulations and experimental measurements of thermoplastic semi-crystalline polyimide R-BAPB synthesized on the basis of dianhydride R (1,3-bis-(3',4-dicarboxyphenoxy) benzene) and diamine BAPB (4,4'-bis-(4″-aminophenoxy) biphenyl) near the SWCNTs on the rheological properties of nanocomposites was performed. We observe the viscosity increase in the SWCNT-filled R-BAPB in the melt state both in computer simulations and experiments. For the first time, it is proven by computer simulation that this viscosity change is related to the structural ordering of the R-BAPB in the vicinity of SWCNT but not to the formation of interchain linkage. Additionally, strong anisotropy of the rheological properties of the R-BAPB near the SWCNT surface was detected due to the polyimide chain orientation. The increase in the viscosity of the polymer in the viscous-flow state and an increase in the values of the mechanical characteristics (Young's modulus and yield peak) of the SWCNT-R-BAPB nanocomposites in the glassy state are stronger in the directions along the ordering of polymer chains close to the carbon nanofiller surface. Thus, the new experimental data obtained on the R-BAPB-based nanocomposites filled with SWCNT, being extensively compared with simulation results, confirm the idea of the influence of macromolecular ordering near the carbon nanotube on the mechanical characteristics of the composite material.

Structure-Property Relationship of Polyetherimide Fibers Filled with Carbon Nanoparticles.

Nanocomposite fibers based on heat-resistant amorphous polyetherimide (PEI) were prepared by twin screw melt micro-extrusion. Vapor-grown carbon nanofibers (VGCFs) and single-wall carbon nanotubes (SWCNTs) were used as fillers which helped to achieve enhanced mechanical properties. The structure and mechanical properties of such nanocomposite fibers were studied. Electron microscopy and melt rheology data revealed a uniform distribution of the nanofillers throughout the volume of the fibers. Wide-angle X-ray scattering showed that the orientational drawing of the nanocomposite fibers led to an improved orientation of the filler particles along the fiber axis. VGCFs or SWCNTs increased the tensile strength and modulus (by ∼275 MPa and ∼5 GPa, respectively) in oriented nanocomposite fibers and decreased deformation at break. SWCNTs were found to be more effective reinforcers than VGCFs.