EFFECT OF AN OXIDATIVE ENVIRONMENT ON THE CREEP COMPLIANCE OF POLY(ETHER URETHANE UREA)

Secondary creep of unstabilized poly (ether urethane urea) (PEUU) in a n oxidative environment appears as a linear time-dependent component s uperimposed on the logarithmic, viscoelastic response. The surfaces of unstabilized PEUU crept in H2O2/CoCl2 have been characterized by scan ning electron microscopy and ATR-FTIR. By examining PEUU crept for var ious periods of time, it is found that surface damage proceeds at grad ually increasing size scales, culminating in large voids. It is hypoth esized that the initial chain scission creates a flaw that grows in si ze under the influence of the applied load into a ''nano-pit,'' which grows further by coalescence into a pit and, finally, a void. The init ial stages of voiding occur during an induction period when there is n o measurable effect on the creep response. It is possible to estimate the average compliance of the damaged PEUU by assuming a composite mod el with an undamaged center layer sandwiched between damaged surface l ayers. When the contribution of the surface layers to the creep compli ance is estimated from the creep curves, the average compliance of the damaged layer is found to be about 1.6 times higher than that of the undamaged PEUU. Independent calculations of the damaged layer complian ce from the void fraction indicate that the damaged layer behaves as a flexible foam in the early stages, then as a more rigid foam at longe r creep times. (C) 1994 John Wiley & Sons, Inc.