Comparisons Among Electrical and Rheological Properties of Melt-Mixed Composites Containing Various Carbon Nanostructures

Abstract

The present investigation compares different carbon-based nanoscaled materials with regard to their effectiveness in producing thermoplastic polymers with antistatic and electrically conductive behavior. The dispersed phases are carbon black (CB) as spherical particles, multiwalled carbon nanotubes (MWNT) as fiber-like filler, and expanded graphite (EG) as platelet-like filler. Each was incorporated into polycarbonate by small-scale melt mixing. The electrical percolation concentrations were found to be 2 wt% for MWNT, 4 wt% for EG, and 8.75 wt% for CB which parallels the aspect ratios of the fillers. For EG a strong dependence of morphology and electrical resistivity on mixing time was observed, indicating a structural change/destruction during intensive shear mixing. Rheological percolation thresholds were found to be lower than electrical percolation threshold for the MWNT and CB, but similar in the case of EG. The general impact on complex melt viscosity decreases in the order MWNT, CB, EG. For EG, at higher loadings (above 4wt%) the viscosity increase with filler content is delayed as is the decrease in resistivity.

Keywords:

• nanocomposites
• carbon black
• expanded graphite
• carbon nanotubes
• melt mixing
• electrical resistivity
• melt rheology

Acknowledgments

We thank Bayer Technology Services (BTS) for help with the SEM and TEM investigations of the nanofillers.

JEM also acknowledges, with gratitude, the financial support provided by the National Science Foundation through Grant DMR-0803454 (Polymers Program, Division of Materials Research).

Notes

*Present address: Petroleum and Chemical Eng. Dept, College of Engineering, Sultan Qaboos University, P.O. Box 33, Al Khod 123, Muscat, Sultanate of Oman.

**Present address: Forest Laboratories, Inc. Plainsboro, NJ, USA