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

Abstract

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 mode I 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 ∼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.