Transient overshoot extensional rheology of long-chain branched polyethylenes: Experimental and numerical comparisons between filament stretching and cross-slot flow

Abstract

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A new look at extensional rheology of low-density polyethylene

“…We believe the stress measured by the EVF is too low, especially at low strain rates, which was also observed by Hoyle et al [12] where the filament stretching measurements were compared with the Sentmanat elongational rheometer measurements. Thus forǫ = 0.01s −1 in Figure 3(b) , there is deviation already from ǫ = 0.5, while forǫ = 2.5s −1 , the EVF measurement agrees with the DTU-FSR measurement up to ǫ = 3.5.…”

“…A maximum in the transient extensional stress of LDPE was observed by several groups [8,9,10]. Steady stress following the stress overshoot was reported firstly by Rasmussen et al [11] and has been experimentally confirmed by comparing the measurements from the filament stretching rheometer and the cross-slot extensional rheometer [12], as well as by comparing the constant stretch rate and constant stress (creep) experiments [13]. Several models have been developed [12,14,15] for the attempt to understand the physics behind the stress overshoot.…”

“…Steady stress following the stress overshoot was reported firstly by Rasmussen et al [11] and has been experimentally confirmed by comparing the measurements from the filament stretching rheometer and the cross-slot extensional rheometer [12], as well as by comparing the constant stretch rate and constant stress (creep) experiments [13]. Several models have been developed [12,14,15] for the attempt to understand the physics behind the stress overshoot. However, none of the models can be practically used for predicting the rheological behavior of LDPEs in industry, since the models contain numerous fitting parameters which are not directly related to molecular structures.…”

Numerical prediction of nonlinear rheology of branched polymer melts

“…Finally, we note that recent experiments on branched polyethylene resins have indicated that there may be stress overshoots prior to the steady state in extensional flow [Wagner and Rol on-Garrido (2008); Alvarez et al (2013); Hoyle et al (2013)], though others dispute these findings [M€ unstedt and Star y (2013)]. To date, a detailed molecular explanation of the stress overshoots appears to be lacking [for example, the model in Hoyle et al (2013) is phenomenological].…”

“…To date, a detailed molecular explanation of the stress overshoots appears to be lacking [for example, the model in Hoyle et al (2013) is phenomenological]. In this work, our focus has been on developing nonlinear rheology predictions based on molecular structure.…”