Thermorheological analysis of blend of high- and low-density polyethylenes

The effect of temperature on dynamic viscoelastic properties of high density polyethylene and low density polyethylene blends with different weight fractions was investigated in the molten state by means of small amplitude oscillatory shear rheometry. It was found that the blends at various compositions do follow well the time-temperature superposition principle and show thermorheologically simple behavior. This behavior is attributed to both similarity in glass-transition temperature of the constituents and phase stability in the blends at various temperatures. The latter was suggested via coincidence of G′-G′′ plots and δ-G^* plots at different temperatures. That was furthur supported using G′ vs. temperature curves which showed no breakdown in the linear relation. Horizontal shift factors, which reflect temperature dependence of relaxation times, obtained to draw G′ and G′′ master curves, followed an Arrhenius equation with temperature. Analysis of terminal relaxation times of components revealed that terminal dynamics of components is similar at limited particular temperatures but different at others. Moreover, depending to test temperature, dynamics of a given component in the blend may be faster or slower than in the pure state.