TRANSIENT EXTENSIONAL RHEOLOGY AND THE INFLUENCE OF STRAIN HISTORY

This paper presents new experimental results on the measurement of tra nsient extensional viscosity (TEV) and on the three-dimensional (3D) s urface formed when TEV, strain and time of deformation data are plotte d. In order to test the validity of the hypothesis that such 3D surfac es are unique for a particular polymer at a given temperature, a terpo lymer of 2-ethyl hexyl acrylate, n-butyl acrylate and acrylic acid has been extended at varying rates including step changes in rate of exte nsion. These experiments also throw light on the influence of strain h istory on extensional viscosity. It is shown that a step drop in rate of extension, produces a step increase in TEV which then relaxes back on to the 3D surface. A step increase conversely causes a step fall in TEV with a subsequent rise back to the original surface. The results support the view formed from previous experimental results that these surfaces are a valid representation of TEV although alternative method s of forming the plots should also be considered. Prior straining is s hown to be significant only during the period in which the fluid is re laxing from previous deformation modes. (C) 1998 Elsevier Science B.V. All rights reserved.