Behaviour of unfilled and filled rubbers in shear in the glass-rubber transition region

Summary

Rubbers filled with high amounts of a hard inorganic filler still show the typical mechanical properties of a high polymer, viz. a glass-rubber transition region, a glassy state and a rubbery state. The influence of filler characteristics on the glass-rubber transition is discussed, chiefly on the basis of the course of shear modulus at constant frequency as a function of temperature.

The influence of volume content of filler on the glass-rubber transition of composite materials consists chiefly in a change of the levels of the shear modulus in the glassy and in the rubbery state. This change may be described by a simple macroscopic model due toVan der Poel. Predictions by this theory could be confirmed for rubbers filled with single filler fractions in the range of filler size between 30–500 μm, and in the range of filler content between 0–50 vol.%.

At smaller particle sizes, an influence of filler size was observed, which points to an increase in the transition temperature and to an increase in the level of modulus in the rubbery state with decreasing filler size.

The preparation of composite materials with high filler contents (> 55 vol.%) is only possible by using a filler with a bimodal size distribution.

In this case, moduli depend on filler content and mixing ratio of coarse to fine filler fraction; theVan der Poel theory then gives predictions which are too high in comparison with experimental results.