Abstract
The decay of crosslinked epoxy resin acrylic polymer films under stress was studied. Stress relaxation in hot water was found to fit well with a function consisting of three exponential decay terms. Polymer systems with higher amount of epoxy resin gave lower rate of decay, or a higher proportion of the term of longer relaxation time, indicating the difference in the type of crosslinking. It is considered that different types of crosslinking give relaxations of different decay rates (k1, k2 and k3), and the fractions (A, B and C) of the three decay terms are dependent on the ratio at which those different crosslinks exist.
Stress decay in boiling water proceeds about twice as fast as in air at the same temperature. This is considered to be due to some scissions of bonds caused by water in addition to thermal degradation that occur both in air and in water. The rate of stress decay increased when epoxy resin of higher molecular weight was used.
The activation energies of stress decay term were estimated. The values are 30.9 and 6kcal/mol for polymer systems of zero (k1) and 10% (k2) epoxy resin, respectively.
