PHYSICAL AGING OF PLASTICIZED POLYMER GLASS. W. H. Han and G. B. McKenna, Polymers Division, Building 224, Room A209, NIST, Gaithersburg, MD 20899 (301-975-3207, email:

It is well known that when small molecules are dissolved into polymers a substantial decrease in the glass transition temperature of the polymer commonly occur. In industrial application and daily use polymers and composites are constantly exposed to small plasticizing molecules, most commonly, water. We study the impact of moisture on the viscoelastic response of a model epoxy system. Thin strip samples were subjected to constant humidity(H1) and temperature environments to reach the equilibrium. Then, the physical aging behavior of the samples was monitored using a multi-step creep compliance test machine inside a constant humidity (H2) chamber set at constant temperature. Both humidity up-jump (H1<H2) and down-jump (H1>H2) experiments were performed. The evolution of viscoelastic response in uniaxial creep at different aging times for the humidity jump experiments showed surprisingly similar behavior compared to those observed in temperature jump experiments. In the humidity up and down jumps to the same intermediate humidity, strong memory effect was observed which is typical of glass forming materials for two-temp temperature jump experiments. The results demonstrated the possibility of treating moisture content variation in epoxies in a manner similar to that used to treat temperature changes.