(694c) Quantifying the Effects of Aging on the Viscoelastic Behavior of Flexible Polyurethane Foams

The thermal-mechanical properties of flexible polyurethane foams have been shown to evolve with age creating questions as to the appropriateness of reusing these materials in critical applications. For example, the room temperature shear modulus of a polyurethane foam sample approximately 30 years old was recently shown to have increased approximately 60% from its newly manufactured state. The increase in stiffness was accompanied by a broadening of the glass transition region which increases the viscoelasticity expected under normal service environments and temperatures. In many applications this change in properties could result transportation or other environments that exceed those originally specified.

Here we present thermal-mechanical characterizations of several densities of flexible polyurethane foam as well as a comparison of new and aged foam properties, where available. We also present efforts to quantify the effects of age (via chemical oxidation) on the thermal-mechanical behavior of these foams in an effort to link the degree of chemical oxidation to changes in mechanical properties. Linking chemical changes to mechanical property changes will allow predictions of acceptable service life in oxidative environments. Further, a discussion on current modeling efforts aimed at capturing flexible foam viscoelastic behavior using the simplified potential energy clock (SPEC) model is presented.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.