Mechanical properties of epoxy composites reinforced with a low volume fraction of nanosilica fillers

In this paper we focus on the preparation and mechanical properties of the nanosilica-reinforced, epoxy resin Epikote 828LVEL. Epoxy composites containing two sizes of spherical silica nanoparticles, 130 nm and 30 nm, were prepared at a fixed volume fraction (V-P = 0.5%). To prevent agglomeration, the silica fillers were initially pre-treated with diglycidyl ether of bisphenol A (BADGE). Due to the low content of silica fillers, their inclusion in the matrix was confirmed by the increased roughness of a fracture surface compared to the smooth surface of the neat epoxy. Raman spectroscopy was employed to obtain additional information about the crack-propagation path. The mechanical properties, characterized by a three-point bending test, revealed a 10-20% increase in the composite's modulus of elasticity with 30-nm and 130-nm silica-filler inclusions. Elongation at break, on the other hand, decreased for 5-10% in both composites compared to neat epoxy, suggesting brittle fracture behavior in silica/epoxy composites. The fracture toughness results showed a 25-30% improved toughening for both composites compared to the pure epoxy. The composite's resistance to failure in terms of the impact energy was, however, strongly dependent on the size of the silica: we observed a 30% increase for the 130-nm, and a 60% increase for the 30-nm, silica/epoxy composites, compared to the pure epoxy. (C) 2012 Elsevier B.V. All rights reserved.