Viscoelastic melt rheology and time–temperature superposition of polycarbonate–multi-walled carbon nanotube nanocomposites

Gabriel Y H Choong,Davide S A De Focatiis,David G Hassell

doi:10.1007/s00397-013-0706-6

Gabriel Y H Choong, Davide S A De Focatiis + Show 1 more

Open Access

https://doi.org/10.1007/s00397-013-0706-6

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Abstract

Abstract 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 timescales scale with molar mass in the same way, evidence that the 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.

Highlights

The addition of multi-walled carbon nanotubes (MWCNT) to polymeric matrices has stimulated significant interest within the research and industrial communities
The normalisation is intended to facilitate the determination of a strain amplitude for which both filled and unfilled PC are within the linear viscoelastic (LVE) region
The presence of MWCNTs causes an increase in Tg for most polymers, Castillo and co-workers (2011) observed a reduction in Tg in a wide range of PC nanocomposites similar to those of this study and attributed its presence either to matrix degradation or to favourable interactions between PC and MWCNTs leading to a reduction in the degree of entanglement of chains near the CNT surfaces

Summary

Introduction

The addition of multi-walled carbon nanotubes (MWCNT) to polymeric matrices has stimulated significant interest within the research and industrial communities. The aim is to elucidate the roles played by nanotubes and by the matrix polymer on several aspects of the viscoelastic response: time– temperature superposition and vertical shifting, dynamic strain amplitude, relaxation processes, and strain and temperature history.

Results

Conclusion