Mechanical Characterization of Nanosilica/Epoxy Nanocomposites

Poor compression strength and interlaminar properties, which are matrix related properties, are the limitations of fiber reinforced composites. One approach to enhance mechanical as well as multifunctional properties of fiber reinforced composites is through modifying the polymer matrix by nano-sized fillers. This paper focuses on improving the mechanical properties of the matrix by reinforcing with nanosilica, while the reinforced matrix will be later used in fiber reinforced composites. The matrix chosen was SC79 epoxy and the nanofiller chosen was Nanopox F400 supplied by Nanoresins AG, Germany. Nanocomposites were made by mixing SC79 epoxy resin, Nanopox F400, and curing agent using a mechanical stirrer, followed by curing. TEM analysis showed uniform dispersion of silica nanoparticles with the size of the majority of the nanoparticles in the range of 14 to 21 nm. Dynamic mechanical analysis and ASTM standard tension, compression, shear and plane-strain fracture toughness tests were conducted. Storage, tensile, compressive, and shear modulus as well as the fracture toughness of the nanocomposites increased monotonically with the addition of nanosilica. For 20% wt. nanosilica, the improvement in tensile, compressive and shear modulus was 20%, 20% and 17%, respectively, and fracture toughness increased by 30%. The 0.2% offset tensile and compressive strengths as well as Poisson’s ratio did not change with the addition of nanosilica. The comparison of experimental tensile and compression moduli agreed well with the predicted data from Halpin-Tsai equation and also with the literature. The results presented in this paper are encouraging to use the material in fiber reinforced composites.