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Abstract
Non-modified Multiwalled Carbon Nanotubes (MWCNT) and polypropylene (PP) in absence of compatibilizer have been chosen to elaborate MWCNT/PP nanocomposites using a simple melt-mixing dispersing method. Calorimetry results indicate little effect of MWCNTs on crystallinity of PP, revealing not much interaction between nanotubes and PP chains, which is compatible with the employed manufacturing procedure. In any case, a hindering of polymer chains motion by MWCNTs is observed in the molten state, using oscillatory flow experiments, and a rheological percolation threshold is determined. The percolation limit is not noticed by Pressure-Volume-Temperature (PVT) measurements in the melt, because this technique rather detects local motions. Keeping the nanocomposites in the molten state provokes an electrical conductivity increase of several orders of magnitude, but on ulterior crystallization, the conductivity decreases, probably due to a reduction of the ionic conductivity. For a concentration of 2% MWCNTs, in the limit of percolation, the conductivity decreases considerably more, because percolation network constituted in the molten state is unstable and is destroyed during crystallization.
Highlights
In their seminal review of 2006 [1], Moniruzzaman and Winey stated that the fabrication methods of carbon nanotubes (CNT)/polymer nanocomposites were focused on improving CNT dispersion, because a better dispersion in the polymer matrixes was found to improve properties
The obtained original results are organized to respond to the following issues, scarcely treated in the literature: (a) Effect of Multiwalled Carbon Nanotubes (MWCNT) on the crystallization process of PP, when neither compatibilizers, nor functionalized carbon nanotubes are used; (b) Rheological percolation observed in the terminal or flow region of dynamic viscoelastic measurements; (c) Capacity/inability of PVT measurements to detect a percolation threshold; (d) Effect of the MWCNT concentration on the electrical conductivity increase observed during annealing in the molten state; (e) Effect of the MWCNT concentration on the electrical conductivity decrease observed during crystallization
A nucleating effect of the MWCNTs is noticed by a reduction of the crystallization time, this reduction becoming more evident as the temperature of the isothermal measurement is increased
Summary
In their seminal review of 2006 [1], Moniruzzaman and Winey stated that the fabrication methods of carbon nanotubes (CNT)/polymer nanocomposites were focused on improving CNT dispersion, because a better dispersion in the polymer matrixes was found to improve properties. We have to recognize that the efforts to reach a good CNT dispersion, modifying MWCNTs and/or using compatibilizers, to fabricate MWCNT/PP nanocomposites do not necessarily bring better electrical conductivity results [27,28,29,30,31] than when neat components are adequately melt mixed and submitted to annealing in the molten state. In this regard, the results obtained by Lee et al [12] are significant. The obtained original results are organized to respond to the following issues, scarcely treated in the literature: (a) Effect of MWCNTs on the crystallization process of PP, when neither compatibilizers, nor functionalized carbon nanotubes are used; (b) Rheological percolation observed in the terminal or flow region of dynamic viscoelastic measurements; (c) Capacity/inability of PVT measurements to detect a percolation threshold; (d) Effect of the MWCNT concentration on the electrical conductivity increase observed during annealing in the molten state; (e) Effect of the MWCNT concentration on the electrical conductivity decrease observed during crystallization
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