Evaluation of branched polypropylene degradation by using different constitutive equations

In this work, virgin as well as thermally degraded branched polypropylenes were investigated by using rotational and Sentmanat extensional rheometers. Based on the shear and extensional rheology data it was deduced that both chain scission and chain branching takes place during thermal degradation of the tested polypropylene. It was found that simple constitutive equations such as Generalized Newtonian law, modified White-Metzner model and Yao model can be used to describe the measured steady state shear and uniaxial extensional viscosity data. It was revealed that Yao and Generalized Newtonian models have capability to quantify level of extensional strain hardening (i.e. the maximum steady state uniaxial extensional viscosity divided by 3 times Newtonian viscosity) as a function of degradation time via their parameters not only quantitatively but also qualitatively