CREEP OF A POLY(ETHERURETHANE UREA) IN AN OXIDATIVE ENVIRONMENT

The creep behavior of a PEUU without added stabilizers was examined in H2O2/CoCl2, an environment that simulates the biodegradation of this polymer. Creep in the control environments, air, water, and H2O2, was logarithmic with time as is characteristic of primary or viscoelastic creep. At short times, creep in H2O2/CoCl2 followed the same time depe ndency as creep in H2O2; however, at longer times an acceleration in t he creep rate was observed. Creep in H2O2/CoCl2 was satisfactorily des cribed by addition of a Linear time term to the creep equation with an induction time, t(i) The induction time was extended by stress-induce d crystallization of the soft segments, but was reduced by an increase in H2O2 concentration. Oxidative degradation of the PEUU soft segment s was detected by infrared and GPC analysis at times less than t(i). T his led to the speculation that an initial ''precursor'' layer was cre ated at the surface by chain cleavage. Microcracking in a subsequent s tage was postulated to be responsible for the observed effect on the c reep behavior. (C) 1994 John Wiley and Sons, Inc.