Creep and Dynamic Mechanical Properties of Filled Polyethylenes

The creep and dynamic mechanical properties are reported for a series of filled and unfilled polythylenes. The fillers (untreated and treated with silanes) were kaolin and wollastonite. The variables studied include filler concentration, silane treatment, water soaking, temperature, and load. Most of the creep data can be explained, and semiquantitatively predicted, in terms of the increase in elastic modulus of the materials as a result of the incorporation of the filler. However, there are some secondary effects due to filler-polymer interactions which apparently change the properties of the polymer phase and result in a further reduction of creep and an increase in damping. The presence of the filler greatly reduces creep, increases the stiffness, and increases the loss modulus of polyethylenes. Silane treatment generally reduces creep and increases modulus somewhat. An unexpected long-time aging effect at room temperature was found which makes the polyethylenes more creep resistant. If allowance is made for the aging effect, soaking in water increases the creep of filled polyethylenes.