On modeling the composition dependence of the bulk viscosity of immiscible polymer blends

The purpose of this article is to clear the confusion in the literature on the following two issues: (1) determination of the bulk viscosity of immiscible polymer blends using a plunger‐type capillary viscometer and (2) modeling the composition dependence of the bulk viscosity of immiscible polymer blends. Related to the first issue, it is pointed out that measurement of the total pressure drop across the entire length of a capillary die, while using a plunger‐type viscometer, to determine the bulk viscosity of an immiscible polymer blend is not justified. This is because the morphology (the state of dispersion) of an immiscible polymer blend varies along the axis of a capillary die. Related to the second issue, it is pointed out that the use of such empirical expressions as inverse additivity or logarithmic additivity relationships is of no rheological significance to determine the composition dependence of the bulk viscosity of immiscible polymer blends. This is because such empirical expressions do not contain terms describing the state of dispersion of an immiscible polymer blend. A computational approach is suggested, though formidable but not insurmountable, which will lead to establishing rheology–morphology–processing relationships in immiscible polymer blends. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers