Impressive Fatigue Life and Fracture Toughness Improvements in Graphene Oxide/Epoxy Composites

Epoxy systems have proven popular having important applications in aerospace and wind energy, but fracture and fatigue resistance of this polymer remain less than desired. Graphene oxide, a form of atomically thin carbon, possessing impressive multifunctional properties and an ideal interface for interacting with polymer matrices, has emerged as a viable reinforcement candidate. In this work, we report enhancements of 28-111% in model fracture toughness and up to 1580% in uniaxial tensile fatigue life through the addition of small amounts (<= 1 wt %) of graphene oxide to an epoxy system. Graphene oxide was uniquely synthesized by unraveling and splaying open helical-ribbon carbon nanofibers. The resulting oxygenated basal planes and edges of the graphene oxide sheets were observed to promote onset of the cross linking reaction and led to an increase in total heat of reaction effecting slightly higher glass transition temperatures of the cured composites. Measured improvements were also detected in quasi static tensile and flexural stiffness and strength. The addition of only 0.1 wt % graphene oxide yielded a similar to 12% increase in tensile modulus. At 1 wt %, flexural stiffness and strength were 12 and 23% greater than the unmodified epoxy. Sheets were observed to be well dispersed and at various orientations within the matrix, enabling their large, 2D, and zero bulk dimensions to pin incipient matrix cracks, a toughening mechanism not typically detected in nanocomposites.