Preferentially fixing nanoclays in the phases of incompatible carboxylated nitrile rubber (XNBR)-natural rubber (NR) blend using thermodynamic approach and its effect on physico mechanical properties

Abstract

This work reports a unique thermodynamic approach for preferentially fixing nanoclays in the phases of incompatible carboxylated nitrile rubber (XNBR)/natural rubber (NR) blends prepared by solvent casting method. Projected for the first time in the area of polymer blend research, this study investigates different parameters, like (i) solubility parameter values of constituent blend components, nanoclays and solvents, (ii) interaction parameter (χ) values between the individual blend components/solvents and nanoclays/solvents, and (iii) difference in interaction parameter (χ) value between the constituent blend component/solvent and nanoclay/solvent and identifies their role in preferentially fixing nanoclays in the respective blend phases. For example, 83% of Cloisite 15A nanoclay (at 8 phr) is found in NR phase (when toluene is used as the solvent for dissolving the rubbers and for dispersing nanoclay) since the difference in interaction parameter value (0.04) between χNR/toluene−χCloisite 15A/toluene is lower when compared to the difference in interaction parameter value (0.17) between χXNBR/toluene−χCloisite 15A/toluene. Similarly, by judiciously choosing different solvents for dissolving the rubbers and for dispersing nanoclays it was possible to preferentially move nanoclay particles to different phases of XNBR/NR blend. The preferential fixing of nanoclays in a particular phase using the thermodynamic approach was quantified by dynamic mechanical analysis (DMA), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Selectively fixing the right nanoclay in the dispersed phase mutilated and suppressed the coalescence rate of the dispersed phase, which in turn lead to significant improvement in the overall properties.