Elastic behavior of LDPE/HEPE blend melts in capillary extrusion

The studies of the elastic behavior in the capillary flow of LDPE/HDPE blend melts were carried out at a test temperature range from 180 to 200°C and at an apparent shear rate of about 25–120 s−1. The end-pressure drop (ΔPend) increased nonlinearly with increasing wall shear stress (τw) and achieved a minimum value at a weight fraction (ϕHD) of HDPE of 50%. The die-swell ratio (B) increased basically linearly with increasing τw or ΔPend and achieved a maximum value at ϕHD of 50%. With the addition of the die length–diameter ratio, the values of B were decreased linearly. At a low shear rate, the temperature sensitivity of the melt die-swell was more significant than at a high shear rate. With increasing ϕHD, B increased when ϕHD < 50%, then decreased. B reached a maximum value at ϕHD of 50% and a fixed apparent shear rate. This phenomenon may be explained by using the theory of viscoelastic competition between components of polymer blend melts. Furthermore, the first normal stress difference (N1) of the sample melts was estimated by using an equation published in a previous work. The results showed that B increased linearly with increasing N1.