Since its recent successful isolation, graphene has attracted an enormous amount of scientific interest due to its exceptional physical properties. Graphene incorporation can improve electrical and mechanical properties of polymers including polyethylene (PE). However, the hydrophobic nature and low polarity of PE have made effective dispersion of nano-fillers difficult without compatibilization. Graphene was derived from graphite oxide (GO) via rapid thermal exfoliation and reduction. This thermally reduced graphene oxide (TRG) was blended via melt and solvent blending with linear low density PE (LLDPE) and its functionalized analogs (amine, nitrile and isocyanate) produced using a ring-opening metathesis polymerization (ROMP) strategy. TRG was well exfoliated in functionalized LLDPE while phase separated morphology was observed in the un-modified LLDPE. Transmission electron micrographs showed that solvent based blending more effectively dispersed these exfoliated carbon sheets than did melt compounding. Tensile modulus was higher for composites with functionalized polyethylenes when solvent blending was used. However, at less than 3 wt.% of TRG, electrical conductivity of the un-modified LLDPE was higher than that of the functionalized ones. This may be due to phase segregation between graphene and PE, and electrical percolation within the continuous filler-rich phase.
Bibliographical noteFunding Information:
Financial support from the Abu Dhabi-Minnesota Institute for Research Excellence (ADMIRE) is acknowledged. The authors also appreciate Dr. Craig Silvis at Dow Chemical Co. for providing Affinity EG-8200 and MA grafted EG-8200, and Adam D. Reimnitz and Darius B. Jaya for their help on melt processing and property measurements. SK thanks Abdul Aziz Al Hajeri for his help in functionalized PE syntheses. Parts of this work were performed in the College of Science and Engineering Characterization Facility and the Polymer Characterization Facility at the University of Minnesota, which receive partial support from NSF through the MRSEC program.
- Polymer nanocomposites