Phase continuity detection and phase inversion phenomena in immiscible polypropylene/polystyrene blends with different viscosity ratios

Blends of polypropylene (PP) and polystyrene (PS) were prepared in a twin-screw extruder and studied in a wide range of compositions. Phase continuity was first determined using selective solvent extraction. Subsequently, dynamic stress rheometry and dynamic mechanical analysis were used to detect the co-continuity and phase inversion compositions in the melt and the solid states. It appears that the phase inversion occurs in a domain rather than at a single point. The evaluation of the storage modulus of PP/PS blends in the melt at a constant low frequency gives information about the co-continuity, as far as the onset of co-continuity and phase inversion composition of the PS phase are concerned. The evaluation of the storage modulus and mechanical loss factor at a constant high temperature, or the glass transition temperature intensity allowed to precisely detect the phase inversion composition. The fractionated or bulk crystallization behavior of the crystallizable PP phase in the PP/PS blends can also be used to identify the matrix/dispersed phase or co-continuous phase morphology. Several semi-empirical models using the dynamic viscoelastic properties of blend components have been applied to detect the phase inversion composition. An extensive data set presented, can also be used to guide future modeling.