Barium sulfate–filled blends of polypropylene and polystyrene: Microstructure control and dynamic mechanical properties

Abstract The microstructure of filled blends consisting of a semicrystalline polypropylene homopolymer (PP) matrix and a polystyrene (PS) dispersed phase with barium sulfate (BaSO ₄ ) filler can be controlled by an addition of maleic anhydride‐grafted polypropylene (PP‐g‐MAH) or styrene‐maleic anhydride copolymer (SMA). Scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA) in the solid and melt states were the analytical tools used. The filler is occluded at the interface of the polymer phases in the filled blend without PP‐g‐MAH or SMA. The addition of BaSO ₄ to the PP/PS blend results in a decrease in domain size of the minor polymer phase. The filler is occluded in the PP phase when PP‐g‐MAH is added, while SMA results in the occlusion of the barium sulfate filler in the PS phase. The results of the SEM and the DMA studies were correlated, with indications of a filler network structure with both the PP‐g‐MAH and SMA modifiers. The barium sulfate filler surface has a specific affinity to maleic anhydride copolymers. The BaSO ₄ filler alone did not have a nucleation effect on the PP; however, in combination with PP‐g‐MAH, a clear nucleation effect was observed.