1992 Volume 48 Issue 10 Pages 521-526
Elongational viscosity was measured at constant strain rates and at the temperature of 160°C for the melt samples of low density polyethylene (LDPE), high density polyethylene (HDPE), and their blends, which showed almost same curves in the frequency dependence of complex viscosity ranging from 10-2 to 102 rad/sec at the same temperature. Non-linearity of the elongational viscosity of the samples was evaluated by non-linearity parameter, defined as the ratio of the measured elongational viscosity to the expected viscosity assuming the linear viscoelasticity. Elongational viscosity at linear viscoelastic region and intensity of non-linearity of the elongational viscosity, defined as the slope of the linear relationship between natural logarithm of the non-linearity parameter and total strain, showed deviation from the additivity rule of the weight content of LDPE component at 10, 20 and 80wt%. These three blends were considered to be immiscible in the melt state. Dependence of the intensity of non-linearity upon the weight fraction of LDPE showed qualitative consistency with that of relaxation moduli upon the weight fraction of LDPE at relaxation times as long as 103 and 104 sec, which was calculated by a constitutive equation with Lodge model from the time dependence of the elongational viscosity of the samples.
