Elastic behavior of LDPE/HEPE blend melts in capillary extrusion

The studies of the elastic behavior in the capillary flow of LDPE/HDPE blen d melts were carried out at a test temperature range from 180 to 200 degree s C and at an apparent shear rate of about 25-120 s(-1). The end-pressure d rop (Delta P-end) increased nonlinearly with increasing wall shear stress ( tau(omega)) and achieved a minimum value at a weight fraction (phi(HD)) of HDPE of 50%. The die-swell ratio (B) increased basically linearly with incr easing tau(omega) or Delta P-end and achieved a maximum value at phi(HD) of 50%. With the addition of the die length-diameter ratio, the values of B w ere 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 in creasing phi(HD), B increased when phi(HD) <50%, then decreased. B reached a maximum value at phi(HD), of 50% and a fixed apparent shear rate. This ph enomenon may be explained by using the theory of viscoelastic competition b etween components of polymer blend melts. Furthermore, the first normal str ess difference (N-1) of the sample melts was estimated by using an equation published in a previous work. The results showed that B increased linearly with increasing N-1. (C) 2000 John Wiley & Sons, Inc.