Visualization and microscopic modeling of phase inversion during compounding

A detailed description of the sequence of deformation steps leading to phase inversion during compounding in a low‐viscosity‐ratio co‐polyester/polyethylene blend is presented. Visualization using a glass window and sampling of the blend at different mixing times enabled identification of the intermediate morphologies of the major component en route to phase inversion. Based on these observations, a theoretical model is developed to predict the time to phase inversion. The model incorporates a simplified flow‐field approximation and the calculation of strain imparted to the major component domains. A strain‐based criterion for phase inversion is then proposed, which, in conjunction with the model, yields an explicit expression for the time to phase inversion during compounding, t P.I. . The model predictions are seen to be in good agreement with the increase of t P.I. , on scaleup between two mixing bowls. The correct functional dependence of t P.I. on the nominal maximum‐shear‐rate is predicted. Using combination of pure drag and planar extensional flow, the model predictions are shown to be consistent with the observed dependence of t P.I. on the volume fraction of the minor component and the blend viscosity ratio.