Rheological Evaluation of Petroleum Jelly as a Base Material in Ointment and Cream Formulations : Linear Viscoelastic Behavior

ABSTRACT − The objective of the present study is to systematically characterize a linear viscoelastic behavior of petro-leum jelly in small amplitude oscillatory shear flow fields correspondent to the rheological ground state. With this aim, usinga strain-controlled rheometer, the dynamic viscoelastic properties of commercially available petroleum jelly have been mea-sured at 37 o C (body temperature) over a wide range of angular frequencies at an extremely small strain amplitude of 0.1%. In this article, the linear viscoelastic behavior was reported in detail and then explained from a structural view-point ofpetroleum jelly and discussed in depth with respect to the consumer’s requirements. Main findings obtained from this studycan be summarized as follows : (1) The storage modulus is always greater than the loss modulus over an entire range ofangular frequencies studied, meaning that the linear viscoelastic behavior of petroleum jelly is dominated by an elastic naturerather than a viscous nature. (2) Petroleum jelly shows a desirable linear viscoelastic behavior with respect to the consumer’srequirements because it is undesirable for the product to flow down from the skin at an initial stage upon contact with thehuman skin. (3) A fractional derivative model shows an excellent applicability to describe a linear viscoelastic behavior ofpetroleum jelly. However, this model should be used with a special caution because there exists no physical meaning forthe model parameters. (4) A modified form of the Cox-Merz rule gives a good ability to predict the relationship betweensteady shear flow properties (nonlinear behavior) and dynamic viscoelastic properties (linear behavior) for petroleum jelly.Key words