Molecular orientation and strain in injection moulding of thermoplastics

Obtaining reliable predictions for molecular orientation is currently one of most challenging targets in the simulation of the injection moulding process, being the starting point toward a better understanding of how crystallisation kinetics and final morphology are influenced by flow fields during processing. Although pressure and velocity distribution can be satisfactorily described by viscous models, the viscoelastic nature of the polymer needs to be accounted for in the description of molecular orientation evolution. In this work, different choices for the dumbbell model are adopted to describe the evolution of molecular orientation by effect of kinematics obtained by a viscous approach. Comparison with literature data of birefringence distributions in injection moulded disks identifies one of the choices which correctly describes main features of data.