Influence of the gel on the morphology of a thermoset polymerized into a thermoplastic matrix, under shear

The relation between the gel point of the thermosetting dispersed phase and the coarsening of the morphology of a thermoplastic/thermoset blend reacted under shear has been investigated. The model system was composed of 60 wt% of polystyrene (PS) and 40 wt% of an epoxy-amine system (diglycidyl ether of bisphenol A — 4,4′-methylenebis [2,6-diethylaniline]). This blend is initially homogeneous and phase separates upon polymerization. The reactive blending process consisted of a sequence of dynamic and static blending modes imposed into an internal mixer. The observation of the morphology before and after the transition from the static to the dynamic mode allowed showing that a short period of time, corresponding to a limited evolution of the conversion around the gel point, influences drastically the development of the morphology. The coalescence and agglomeration phenomena that play a determinant role at low and intermediate epoxy conversion, are stopped when the epoxy drops gel, resulting in a stabilization of the morphology. The transition from a static mode to a blending under shear has also revealed the existence of a distribution of conversion among the epoxy-rich domains, caused by the competition between the continual nucleation process of the epoxy droplets and their growth.