Processing, Morphology and Properties of Graphene Reinforced Polymer Nanocomposites
Thesis defense of Ph.D. candidate Hyunwoo Kim
Department of Chemical Engineering and Materials Science
Advisor: Chris Macosko of IPrime’s Microstructured Polymers program.
Held Wednesday, September 9, 2009, 9:15 a.m., EE/CSci 3-180, University of Minnesota
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A unique combination of excellent electrical, thermal and mechanical properties has made graphene a multi-functional reinforcement for polymers. Exfoliated carbon sheets can be obtained from graphite oxide (GO) via either rapid pyrolysis (functionalized graphene sheets, FGS) or chemical modification (isocyanate treated graphite oxide, iGO). Solvent-based blending led to better dispersion of FGS in thermoplastic polyurethane than melt processing. Polyurethane became electrically conductive at even less than 0.5 wt% of FGS. Up to 10 fold increase in tensile stiffness and 90% decrease in nitrogen permeation of TPU were also observed with only 3 wt% of iGO implying high aspect ratio of exfoliated platelets. Dispersion of melt compounded graphite and FGS in poly(ethylene-2,6-naphthalate) was characterized with electron microscopy, X-ray scattering, melt rheology and solid property measurements. Unlike graphite, dispersion of FGS quantified from different routes spreads over a wide range due to structural irregularity and simplified assumptions for composite property modeling. For polycarbonate, flow-induced orientation reduced property gains by graphene dispersion, while quiescent-state annealing restored rigidity and electrical conductivity of the composites. Micro-structural evolution of FGS in polystyrene through annealing was monitored using melt-state rheological and dielectric measurements. Graphene-based polymer nanocomposites can be a new versatile soft material with numerous benefits.