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: firstname.lastname@example.org)
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.