Strength of epoxy polymers. I. Effect of chemical structure and environmental conditions



The breaking times of two crosslinked epoxy polymers under constant stresses were found to decrease at high temperature and humidity. The effect of humidity is, in terms of Bueche's theory, to increase the jump frequency of the polymer segments and to reduce the number of polymer units in cooperative motion in a jump process. When two epoxy polymers with different segment mobilities are compared at a given temperature, the stress-breaking time relationship shifts toward longer times for the polymer with the higher transition temperature. The relation is also applicable in the presence of absorbed water molecules.