Determination of phase diagram of polyolefin blend nanocomposites by rheological approach: Influence of rheological method and nanoparticles on shifting the phase transition boundary

AbstractIn this research, by using different rheometric methods, the temperatures of phase transition for upper critical solution temperature phase diagram of polyethylene (PE) and poly(ethylene‐co‐vinyl acetate) (EVA) blends and filled systems with organically‐modified nanoclay (ONC) were measured. Since the PE/EVA‐based mixtures are widely applied in the film and foam industries, the evaluation of the phase behavior of these mixtures is of great importance. Microscopic observations show that ONC nanoparticles have a compatibilization role on the biphasic microstructure of PE/EVA. ONC nanoparticles have a remarkable impact on the viscoelastic properties of the EVA phase, leading to a reduction in the asymmetry of the viscoelastic properties of the two polymeric phases. The findings of this work focused on the isochronal dynamic temperature sweep tests on the well‐mixed and phase‐separated nanofiller‐filled systems with different cooling/heating rates indicated that these series of experiments did not have the necessary efficiency to determine the phase separation boundary and spinodal temperatures in thermodynamically equilibrium conditions. By using Han plot and dynamic temperature sweep tests at the minimum possible heating rate, 0.25 K/min, it was proved that by adding nanoparticles to PE/EVA blends, the area of well‐mixed region of the phase diagram did not show a significant increment. The pinning effects of nanoparticles on the polymeric chains and correspondingly, the reduction of molecular dynamics mainly affect the phase separation phenomenon.