A Definition of Plasticity
THE word ‘plasticity’, although one which has attained a state almost of ubiquity in several branches of applied physics and industrial chemistry, has, according to Scott Blair1, never been given a quantitative and dimensional definition. In the technical literature a group of quantitative ‘plasticity numbers’ have taken their place. Such expressions as the Williams plasticity number, or the Goodrich plasticity number (both used in rubber technology), have no quantitative meaning other than that of the reading of a particular type of testing equipment when used in a particular manner, and as such cannot be expressed in C.G.S. units.
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
über Viskosität und Plastizität disperser Systeme
Zusammenfassung1.Die Methode des rotierenden Zylinders ist für die Untersuchungen der Plastizitätskonstanten des Teiges anwendbar.2.Die Theorie des Bingham'schen plastischen Stromes findet in den erhaltenen experimentellen Daten für Teig Bestätigung.3.Es wurden die Kurven der Abhängigkeit der Plastizitätskonstanten (der Flie\festigkeit) und der Bingham'schen Viskositätη von dem Wassergehalt im Teig für vier Sorten Weizenmehl (Mahlergebnis 85 Proz.) untersucht. Es wurde ein Zusammenhang zwischen der refraktometrisch bestimmten Fähigkeit des Mehles, Wasser zu binden, sowie der Wasseraufnahmefähigkeit des Mehles und den Plastizitätskonstanten des Teiges festgestellt.4.Die ausgearbeitete Methode gibt die Möglichkeit, die physiko-mechanischen Konstanten des Teiges zu bestimmen, was der Ausarbeitung neuer Methoden der Produktionskontrolle zugrunde gelegt werden mu\.