The effect of mixing on the modes of dispersion and rheological properties of two‐phase polymer blends in extrusion

摘要

AbstractAn experimental study was carried out to investigate the effect of mixing on the state of dispersion and rheological properties in the two‐phase flow of polymer blends. For the study, blends of polystyrene and polypropylene were used, and two mixing devices were employed: a single‐screw extruder combined with a “static mixer,” and a twin‐screw compounding machine. Materials of various blending ratios were extruded at a constant temperature (200°C) through a capillary die having anL/Dratio of 20 (D= 0.125 in.). The state of dispersion in the two‐phase system was investigated from pictures taken of the microstructure of the extrudate samples. It was found that different mixing devices have a profound influence on the state of dispersion of one polymer in another. Also determined were the rheological properties of the two‐phase system investigated, from wall normal stress measurements. Our results show that, when shear stress is used as a parameter, the melt viscosity goes through a minimum, whereas the melt elasticity goes through a maximum. This is regardless of the type of mixing device employed, although the shapes of the curves are affected by the type employed. It is suggested that shear stress, instead of shear rate, be used in correlating the viscoelastic properties of two‐phase