IRREVERSIBILITY ASSUMPTION OF NETWORK DISENTANGLEMENT IN FLOWING POLYMER MELTS AND ITS EFFECTS ON ELASTIC RECOIL PREDICTIONS

Tanner has suggested a constitutive equation for polymer melts and solutions based on a network rupture hypothesis: entanglements are lost irreversibly in the process of deformation as soon as a limiting strain magnitude is reached. Although this model shows serious defects in describing time-dependent material properties it has the appealing feature of irreversibility. On the other hand the BKZ model (considered here in the simplified version of a separable memory function), being more useful in describing startup experiments, does not possess this feature of irreversibility, leading to largely erroneous results in recovery calculations. An improved version of a single integral constitutive equation is presented, where the irreversibility of the process of network disentanglement is incorporated. Predictions of elastic recoil behavior in elongation and shear are compared with experimental results for a well-characterized LDPE melt. © 1979, The Society of Rheology. All rights reserved.