Effect of the interfacial interaction on the phase structure and rheological behavior of polypropylene/ethylene– octene copolymer/BaSO₄ ternary composites

In polypropylene (PP)/ethylene–octene copolymer (POE)/BaSO 4 ternary composites, two different kinds of phase structures are assumed:(1) POE and BaSO 4 filler are separately dispersed in the PP matrix and (2) POE‐encapsulated filler particles (core–shell structure) are dispersed in the matrix. This depends on the interfacial interaction of the composites. For the design of composites with different interfacial interactions, three routes for the preparation of BaSO 4 master batches were developed. First, a mixture of BaSO 4 , POE, and maleic anhydride (MAH) in a certain ratio was extruded in the presence of dicumyl peroxide and then pelletized. In extrusion, MAH‐functionalized POE was in situ formed to enhance the interfacial interaction between POE and BaSO 4 . Second, a mixture of POE and BaSO 4 was directly extruded and then pelletized. Third, after BaSO 4 was treated with an organic titanate coupling agent, the treated BaSO 4 and POE were blended in extrusion and then pelletized. Scanning electron microscopy observations showed that the core–shell structure in which POE encapsulates BaSO 4 particles is formed through route 1, whereas POE and BaSO 4 are separately dispersed into the PP matrix through routes 2 and 3. The rheological behavior of PP/POE/BaSO 4 ternary composites was studied with a controlled stress rheometer. The results showed that the interfacial interaction in composites with core–shell morphology is the strongest. Interparticle interactions give rise to the formation of interparticle networks; the stronger the network is, the larger the shear yield stress is and the smaller the thixotropic loop area is.