Elongational viscosity of polymer melts

Implementation of a lubricated converging flow technique on a commercial capillary rheometer to determine the elongational viscosity of polypropylene melts was presented by the authors earlier [1,2]. This paper presents the results of extending the strain rates to commercially relevant values and also presents the results for other industrial grade polymer melts such as syndiotactic polystyrene (sPS) and nylon-66 melts. It is shown that polypropylene and sPS melts show strain softening whereas the nylon-66 melts show a strain hardening behavior at intermediate strain rates (1-2 s(-1)). A correlation of molecular weight distribution with the elongational viscosity is apparent but more work is needed to establish definite trends.