This work investigates the linear and non-linear viscoelastic melt rheology of four grades of polycarbonate melt-compounded with 3 wt% Nanocyl NC7000 multi-walled carbon nanotubes and of the matching matrix polymers. Amplitude sweeps reveal an earlier onset of non-linearity and a strain overshoot in the nanocomposites. Mastercurves are constructed from isothermal frequency sweeps using vertical and horizontal shifting. Although all nanocomposites exhibit a second plateau at ~105 Pa, the relaxation times estimated from the peak in loss tangent are not statistically different from those of pure melts estimated from cross-over frequencies: all relaxation times scale with molar mass in the same way, evidence that relaxation of the polymer network is the dominant mechanism in both filled and unfilled materials. Non-linear rheology is also measured in large amplitude oscillatory shear. A comparison of the responses from frequency and amplitude sweep experiments reveals the importance of strain and temperature history on the response of such nanocomposites.
Choong, G. Y., De Focatiis, D. S., & Hassell, D. G. (in press). Viscoelastic melt rheology and time-temperature superposition of polycarbonate – multi-walled carbon nanotube nanocomposites. Rheologica Acta, 52(8), https://doi.org/10.1007/s00397-013-0706-6