Dynamic properties of NR/EVA polymer blends: Model calculations and blend morphology

The dynamic mechanical properties of blends of natural rubber (NR) and the ethylene-vinyl acetate copolymer (EVA), a thermoplastic elastomer, were inv estigated in terms of the storage modulus and loss tangent for different co mpositions, using dynamic mechanical thermal analysis (DMTA) covering a wid e temperature range. Mean-field theories developed by Kerner were applied t o these binary blends of different compositions. Theoretical calculations w ere compared with the experimental small strain dynamic mechanical properti es of the blends and their morphological characterizations. Predictions bas ed on the discrete particle model (which considers one of the components as a matrix and the other dispersed as well-defined spherical inclusions embe dded in the matrix) agreed well with the experimental data in the case of 3 0/70 NR/EVA but not in the case of 70/30 NR/EVA blends. A 50/50 blend, wher e a cocontinuous morphology was revealed by SEM studies, was found to be ap proximately modeled by the polyaggregate model (where no matrix phase but a cocontinuous structure of the two is postulated). (C) 1999 John Wiley & So ns, Inc.