Volume Changes and Dewetting in Glass Bead-Polyvinyl Chloride Elastomeric Composites under Large Deformations

Abstract

Abstract Elastomeric materials loaded with inert filler have Theological properties which, on the one hand, are qualitatively like those of unfilled polymeric materials, but which, on the other hand, are unique to filled systems. Their stress-strain curves usually have several distinct regions which are similar to those for certain unfilled polymeric materials. The curves have an initial region in which the stress increases with strain, and here the modulus depends primarily on the amount of filler and the properties of the binder. In the second region, the stress may be roughly independent of the strain or may increase at a rate markedly less than that in the initial region. The transition between these two regions may be either gradual and hardly perceptible or sharp, with a well-defined yield point. Thus, in these two regions, the stress-strain curves may be like those for typical unfilled rubbers or for plastics, or they may resemble the curves for rubbers at low temperatures, which cold draw or neck. In the third region the stress increases more rapidly with strain than in the second region and continues to increase until the specimen breaks; again, this is similar to what is observed for certain plastics and rubbers. Thus, both filled and unfilled systems can have sigmoidal stress-strain curves which may or may not have distinct yield points. However, filled systems, and especially those in which the binder wets, but does not react chemically with the filler, exhibit the sigmoidal-type stress-strain curve for different reasons than do rubbers and plastics. In filled systems, the binder adheres to the filler initially, which reinforces or strengthens the system. However, in the transition and second regions of the stress-strain curve, adhesive bonds between the filler and binder break, a process called dewetting, and vacuoles form around the filler particles. After the adhesive bonds are essentially all broken, a further increase in strain only stretches the binder further and enlarges the vacuoles.