Measurement of elongational rheology of polymer melts using semi-hyperbolically convergent dies

A number of polymer processing operations, e.g. fiber spmnmg, film blowing, injection molding, and extrusion through converging channels involve a substantial amount of elongational flow. Knowledge of elongational rheology of polymeric materials used in these operations is essential for the understanding and control of these operations. In this research, elongational rheology of polymer melts is measured by a new technique using semi-hyperbolically convergent dies and a capillary rheometer. The viscosity obtained using this technique is an apparent or effective elongational viscosity rather than true elongational viscosity, and it is related to the orientability or resistance to orientation development of polymer melts and solutions. In this work, five samples of low density polyethylene (LDPE), five samples of high density polyethylene (HDPE), fourteen samples of blended nylon-66, and eleven samples of solid-state polymerized nylon-66 are characterized at processing temperatures and strain rates using the mentioned technique. The effect of molecular parameters such as molecular weight, molecular weight distribution, end-group concentrations, and degree of solid-state polymerization on the elongational rheology of these samples is studied.