Nanocomposite adhesives: Mechanical behavior with nanoclay

The major objective for this research was to examine the role of epoxy–clay nanocomposites in the area of epoxy bonding to porous stone (granite) substrates. Two bisphenol A epoxy systems were selected based on the prior work that determined optimal adhesive properties from a larger set of epoxy systems to determine the role of viscosity on the intercalation and exfoliation of the clay tactiods in the epoxy resin. The systems were characterized and mechanically tested at varying levels of intercalated and exfoliated organic clay tactiods. In the first stage of the work, epoxy–clay systems were characterized by wide-angle X-ray diffraction (WAXD) to detect inter-laminar distances of clay layers and to determine if the mixing procedures had indeed dispersed and exfoliated the clay layers sufficiently. The second stage of the work involved examining mechanical properties of the epoxy–nanoclay systems. Fracture behavior was studied using granite stone substrates in notched double lap configuration. Compressing a wedge between the cover plates induced the fracture. Fracture toughness was approximated by the load at fracture. Tensile properties were measured using cast dog bone tensile samples. The better layered silicate nanocomposite performance was seen with the lower viscosity resin. The most noticeable improvements in mechanical properties for the lower viscosity resin system were found to be maximum stress, elastic modulus, and yield stress. Increased toughness and stress whitening at 1% by weight nanoclay loading revealed that the clay can act as a shear-yielding toughening agent in this epoxy system.