School of Engineering and Materials Science
Research Student Awards
PhD Thesis: The effect of incorporation of low molar mass liquids on the dynamic mechanical properties of elastomers under strain
Author: AKUTAGAWA, Keizo
Supervisor(s): Craig Davies
While a great deal of empirical knowledge exists on the effects of liquid additions on the dynamic mechanical properties of rubbers, very few systematic studies have been carried out. This thesis presents such a study of the dynamic mechanical properties of rubbers, some containing different amounts and types of liquid. The measurements were mainly carried out using a simple oscillating beam apparatus capable of measuring very small values of tan accurately for specimens prestrained in tension. Several different materials were used for the study, including cis-polyisoprene, acrylonitrile-butadiene and styrene-butadiene rubbers which were swollen to various extents with liquids having a wide range of viscosity. The dynamic mechanical properties of the swollen rubbers were studied as a function of the magnitude of the prestrain, the deformation, the temperature, and the rubber cross-link density.
The results of these dynamic measurements have shown that the dynamic loss modulus E" of the prestrained rubber was independent of prestrain up to an extension ratio of D. For dry rubbers the value of D decreased with decreasing molar mass between cross-links (Mc) and for swollen rubbers with increasing extent of swelling. In this region, for each liquid-rubber system, the effect of the liquid on E" could be described using the free volume theory here newly applied to swollen cross-linked rubbers. This simple free volume theory based on the additivity of the fractional free volumes of the liquids and the rubbers in the mixture is shown to represent well the temperature dependence of E" and the dependence of E" on the volume fraction of rubber (vr) for the liquids used in this study.