Water sorption kinetics of acrylonitrile-butadiene rubber/poly(ethylene-co-vinyl acetate)/organoclay nanocomposites

Nanocomposites based on acrylonitrile-butadiene rubber (NBR) and poly(ethylene-co-vinyl acetate) (EVA) with several weight ratios (20, 40 and 60 wt% NBR) and 1, 3, 5 and 7 wt% organocaly (OC) were fabricated in an internal mixer. The diffusion of water through the specimens made of the unfilled blends and their nano-composites was studied with special reference to the blend composition and OC content at three temperatures of 25, 40 and 55 degrees C using a gravimetric method. It was found that the transport coefficients, namely, diffusion coefficient (D), sorption coefficient (S) and permeation coefficient (P) increased with increasing of NBR content. In addition, while S and P increased systematically with the OC content, D decreased to some extent with the increase in the nanofiller concentration. The results revealed that the diffusion happened mainly through the polymeric materials. It was also found that the sorption process for all the materials studied was dominated by a Henry sorption mode giving an endothermic process. The change in entropy, enthalpy and free energy of sorption were also calculated using the experimental data. Schematic models were also proposed for water uptake of the blend and its nanocomposite counterpart.