Comparative Rheology of Commercial Viscosity Modifier Concentrates 932834
Viscosity Modifiers (VM's) are commonly sold as polymer in oil concentrates. Thus, the handling (pumpability and mixability) characteristics of these systems are important practical considerations. These VM's normally are characterized only by kinematic viscosity, although they are handled at a range of shear rates/stresses which kinematic viscosity does not describe. New polymer types and structures and the desire to make the modifier level as high as possible requires more than a single point kinematic viscosity measurement. The rheological behavior of the concentrate is required to make economical systems that can be handled in a practical manner.
This paper represents an initial study of viscosity modifier concentrates by rheological techniques. Polymer types studied include olefin copolymers (OCP), dispersant styrene ester copolymers (DSE). polymethacrylates (PMA), radial hydrogenated isoprene (IR), styrene-hydrogenated isoprene (SI) and styrene-hydrogenated butadiene copolymers (SB). Rheological methods include the study of flow properties (shear methods) and dynamic properties (oscillation methods) via controlled stress rheometry. Rheological behavior is classified in general terms by polymer type.
The polymer systems studied are shown to exhibit a wide range of rheological behaviors from nearly Newtonian to highly elastic and shear dependent. Two styrene-butadiene VM's are shown to exhibit unusual temporary shear thickening behavior. A similar VM of lower styrene content does not demonstrate this phenomenon. Temperature, concentration, and base oil types are all shown to affect the behavior of these systems significantly. An explanation for this temporary shear thickening behavior is proposed.