Synergistic effect of exfoliated graphite nanoplatelets and short glass fiber on the mechanical and interfacial properties of epoxy composites

In this study, the properties of hybrid composites made by epoxy reinforced with short glass fibers (GF) and exfoliated graphite nanoplatelets (GNP) were determined as a function of the GF loading. The addition of GNP, either within the matrix or at the GF surface (GFc), promoted the formation of a stronger GF–epoxy interface, as evaluated by the single-fiber microdebonding test, resulting in an increase of the interfacial shear strength by ∼60% exhibited by the hybrid epoxy composite reinforced with 5 wt% GNP. Quasi-static tensile tests and impact tests were performed in order to explore how the combined effect of the nano- and micro- size reinforcements affected the macroscopic mechanical properties under low and high strain rates. The improved tensile modulus, ultimate tensile strength and impact resistance exhibited by the hybrid composites revealed that it is possible to introduce the nano-materials at the fiber/matrix interface and significantly improve the interfacial properties, leading to lighter and stronger composites. Furthermore, the storage modulus and the viscoelastic behavior of GF/epoxy composites were remarkably enhanced upon addition of GNP, indicating strong GNP–polymer interactions and immobilization of the polymer chains. In conclusion, the combined effect of nano-materials and micro-size reinforcements can be exploited to produce light-weight hybrid composites with enhanced mechanical properties.