Aspect ratio effects of multi-walled carbon nanotubes on electrical, mechanical, and thermal properties of polycarbonate/MWCNT composites

Significance statement

The significance of this work is that we show that lower added amounts to achieve electrical conductivity in a thermoplastic nanotube composite are required for nanotubes with higher aspect ratios. However, at the processing conditions given in the paper, a limit exists since longer tubes are broken more during processing then shorter tubes. The numbers next to the symbols in the figure are the aspect ratios before compounding; after compounding aspect ratios 134 and below were reduced in length by a factor of 1.5-2, while 313 and 474 were reduced by a factor of ~5. This work has significant implications in that processors have, in order to get conductivity at the lowest possible loading, designed processing conditions so as to maximize dispersion. What this work shows is that with longer tubes this strategy is not correct; there is an optimal set of conditions that balances dispersion and nanotube breakage.

Journal of Polymer Science Part B: Polymer Physics, Volume 52, Issue 1, pages 73–83, 1 January 2014.

Jiaxi Guo¹, Yanjun Liu¹, Ricardo Prada-Silvy², Yongqiang Tan², Samina Azad²,Beate Krause³, Petra Pötschke³ , Brian P. Grady^1,4,

School of Chemical, Biological & Materials Engineering, University of Oklahoma, Norman, Oklahoma.2.
SouthWest NanoTechnologies Inc. (SWeNT), Norman, Oklahoma.
Leibniz Institute of Polymer Research Dresden (IPF), Dresden, Germany.
Corresponding author: Dr. Brian P. Grady
Professor and Douglas and Hilda Bourne Chair in Chemical Engineering
Director, Institute for Applied Surfactant Research
University of Oklahoma
100 East Boyd; SEC Rm. T-223
Norman, OK 73019-0628
http://coecs.ou.edu/Brian.P.Grady/index.html

Abstract

Two multi-walled carbon nanotubes (MWCNTs) having relatively high aspect ratios of 313 and 474 with approximately the same diameter were melt mixed with polycarbonate (PC) in a twin-screw conical micro compounder. The effects of aspect ratio on the electrical, mechanical, and thermal properties of the PC/MWCNT composites were investigated. Electrical conductivities and storage moduli of the filled samples are found to be independent of the starting aspect ratio for these high aspect ratio tubes; although the conductivities and storage moduli are still significantly higher than values of composites made with nanotubes having more commercially common aspect ratios of ∼100. Transmission electron microscopy results suggest that melt-mixing reduces these longer nanotubes to the same length, but still approximately two times longer than the length of commercially common aspect ratio tubes after melt-mixing. Molecular weight measurements show that during melt-mixing the longer nanotubes significantly degrade the molecular weight of the polymer as compared to very similar nanotubes with aspect ratio ∼100. Because of the molecular weight reduction glass transition temperatures predictably show a large decrease with increasing nanotube concentration. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 73–83

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Aspect ratio effects of multi-walled carbon nanotubes on electrical, mechanical, and thermal properties of polycarbonate/MWCNT composites

Abstract

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