Morphology development of LDPE-PS blend compatibilization

LDPE-polystyrene (PS) blends were compatibilized using three PS-hydrogenated polybutadiene-PS and one PS-hydrogenated polybutadiene block copolymers. The blends were prepared by corotating twin-screw extrusion, then were injection-molded. During processing, the morphology evolution of the blends was studied using SEM and image-analyzing techniques. Different screw profiles were used for extrusion. Under the extrusion conditions and when all the blend constituents had melted, the use of one kneading-disc section resulted in a high mixing effect. The addition of other kneading-disc sections did not increase the dispersion. The flow of the blend, through the extruder die or in the injection mold, induced heterogeneous skin-core structures. The analysis of the evolution of the structure of these blends during processing showed that the addition of a compatibilizer increased their stability. Going from LDPE-rich to PS-rich blends, the morphology evolves from a nodular dispersion of PS in LDPE to a cocontinuous structure. With the addition of a copolymer to a 25-75 wt % LDPE-PS blend, the structure changes from a cocontinuous to a nodular one. Comparing the effect of the different copolymers on the blend morphology, the diblock copolymer results in the most homogeneous and finest dispersions. The stabilization of increasing potential values of the interface surface of these blends requires increasing concentrations of the copolymers. (C) 1996 John Wiley & Sons, Inc.