In this
work, a rheological study of automotive lubricant oils, neutral light
paraffinic (NLP) and neutral medium paraffinic (NMP), additivated with two
commercial viscosity index improvers-VIIs, based on hydrogenated poly
(isoprene-co-styrene), at different concentrations, was carried out. The study
included the determination of the kinematic viscosity of the mixtures, the
calculation of the viscosity indexes and their behavior when subjected to
various rheometric experiments, including stress sweep, steady state flow,
creep and recovery, and temperature ramp oscillatory tests. The obtained
results showed the efficacy of the additives as viscosity index improvers, enabling
a significant increase in the viscosity index of the pure oils at relatively
low concentrations. The determination of the storage (G’) and of the loss (G”)
moduli for the mixtures oil/VII additives showed a large predominance of the
viscous effect over the elastic one. Except when under low shear stress, the
mixtures showed a pseudoplastic behavior, with the flow curves being adjusted
to fit the Ostwald-de-Waele model (Power Law), with negative flow behavior
indexes.