Effect of organically modified nanoclay on the miscibility, rheology, morphology and properties of epoxy/carboxyl-terminated (butadiene-co-acrylonitrile) blend

Abstract

Carboxyl-terminated (butadiene-co-acrylonitrile) (CTBN) modified epoxy/clay nanocomposites (epoxy/clay/CTBN ternary nanocomposites) were synthesized using nadic methyl anhydride as curing agent. Effect of nanoclay on the phase behavior (UCST) of epoxy oligomer/CTBN blend has been studied in detail. The phase diagram was shifted to a higher temperature with increase in clay loading due to the easy penetration of low molecular weight CTBN into the clay galleries. The XRD studies confirmed the penetration of CTBN into the clay galleries, as the ‘d’ spacing increased with increase in CTBN content in the epoxy/clay/CTBN ternary nanocomposite. The interaction of organically modified clay with epoxy and CTBN were studied using frequency sweep rheological analysis. The individual and combined effect of nanoclay and CTBN on the cure reaction was followed by isothermal rheological analysis. It was found that complex viscosity profiles during cure reaction follow an exponential growth. The characteristic relaxation time of viscosity growth was described by the WLF equation. Moreover the dynamics of phase separation during cure was followed using optical microscopy. The scanning electron microscopic (SEM) images revealed that the domain size of phase separated CTBN in epoxy/clay/CTBN ternary nanocomposite was smaller than in epoxy/CTBN binary blend. The kinetic factor in epoxy-anhydride cure reaction and the presence of clay at epoxy–CTBN interface was used to explain this size reduction. The high resolution transmission electron microscopic (HRTEM) image of epoxy/3 phr clay nanocomposite showed that the clay platelets were mostly intercalated. Epoxy/3 phr clay/15 phr CTBN nanocomposite has an intercalated with occasional exfoliated microstructure with slightly distorted clay orientation. Low magnification TEM images showed that most of the clay platelets located near the phase separated CTBN and the presence of clay at the epoxy–CTBN interface. The viscoelastic properties of epoxy/clay/CTBN nanocomposite was studied and compared with that of epoxy/clay nanocomposite and epoxy/CTBN blend. A quantitative measurement of constrained region (macromolecular chains immobilized by the clay platelets) was carried out for epoxy/clay and epoxy/clay/CTBN nanocomposites. Finally thermal degradation studies were performed to evaluate the thermal stability of the ternary nanocomposites.