Synthesis, Characterization and Mechanical Behaviour of Epoxy Nanocomposites Reinforced with Layered Silicates

Abstract

Epoxy-clay nanocomposites have been widely used in application areas like encapsulation of electronic components, industrial coatings, adhesives for bonding, engineering components in aeronautics, protective coatings, high tension electrical insulators, flooring tooling etc. The present work studies the effect of nanoclay addition on the mechanical performance of epoxy based composites. The key issues included synthesis of nanocomposites with changing nanofiller content and their subsequent characterization and evaluation of mechanical properties. Synthesis of nanocomposites comprised of a definite sequence of processing steps involving homogenization and ultrasonication of the clay-epoxy mix, so as to obtain an exfoliated or intercalated morphology. Tensile, impact and microhardness testing were evaluated according to ASTM standards D638–02a, D256–02ε1 and E384–10ε2 respectively. XRD and SEM analysis were performed to study the morphology of the prepared nanocomposites and their subsequent fracture mechanisms involved during mechanical testing. XRD results showed that all nanocomposite formulations, except 0.5 wt. % clay nanocomposite, showed peak in the diffractograms, confirming the presence of intercalated clay structures. The dspacings for pristine clay and 1.5 wt. % clay nanocomposite were 25.07 Å and 34.02 Å respectively. The maximum value of tensile modulus was obtained corresponding to 3 wt. % clay, signifying an improvement of about 63 % as compared to neat epoxy. The peak values for tensile strength, impact strength, and microhardness were obtained corresponding to 1.5 wt. % nanoclay loading as compared to neat epoxy (signifying an improvement of about 48 %, 22 % and 45 % respectively). SEM fractography of tensile fractured surface showed that the fracture surface of neat epoxy was relatively smooth and crack propagation was largely unidirectional indicating brittle type failure. However, the fracture surface of 1.5 wt. % clay nanocomposite was rough, indicating the presence of energy absorption mechanisms like crack deflection, crack pinning, and crack arresting. But, the fractured surface of 3 wt. % clay nanocomposite showed the presence of large agglomerates leading to generation of stress concentration points and decrease in tensile strength. SEM fractography of impact fractured surface of neat epoxy showed that the crack propagation lines were nearly parallel to each other, indicating fast and brittle fracture behaviour. But, the fracture surface of 1.5 wt. % clay nanocomposite showed increased roughness and tortuosity, indicating the presence of similar energy absorption mechanisms as that for tensile fractured nanocomposite.