Polycarbonate composites reinforced with graphite and functionalized graphene sheets (FGS) were produced using melt compounding. Composite samples with different degrees of graphite orientation were processed via injection, compression molding and long-term annealing. Electron microscopy and X-ray scattering revealed that FGS was nearly exfoliated. However, graphite remained multi-layer even after melt processing. Flow induced orientation of graphite was observed from both injection and compression molded samples. Graphite particles in samples after long-term annealing exhibited more random orientation. Composites with the exfoliated FGS required a smaller amount of reinforcement for rigidity and connectivity percolation, as determined by melt rheology and electrical conductivity measurements. FGS also showed better performance in suppressing gas permeability of polycarbonate. However, improvements by FGS dispersion in tensile modulus and dimensional stability were not as significant. This may be due to defects in the sheet structure formed during oxidation and pyrolysis used to exfoliate.
Bibliographical noteFunding Information:
The authors acknowledge research grants from General Motors Corp. and the University of Minnesota Industrial Partnership for Research in Industrial and Materials Engineering (IPRIME). We would like to thank John Lettow of Vorbeck Materials for providing the FGS, Adam Reimnitz for help with melt processing and property measurements, Prof. Michael Tsapatsis at the University of Minnesota for use of the gas permeation apparatus, Mingjun Yuan at Entegris for use of electrical conductivity measurements. Parts of this work were carried out in the University of Minnesota I.T. Characterization Facility, which receives partial support from NSF through the NNIN program and in the Polymer Characterization Facility, which receives partial support from the NSF funded University of Minnesota MRSEC.
- Flow orientation
- Layered graphite nanocomposites
- Melt compounding