Non-Fickian Behavior of Water Absorption in an Epoxy-Amidoamine Network

摘要

The water absorption in a DGEBA-amidoamine network synthesized with an amine excess was studied between 10 and 90% RH at 30, 50 and 70°C. This quasi-ideal epoxy network displays deviations from the classical Fick's behavior after the transient period. The amplitude of these deviations is an increasing function of both the relative humidity and temperature. In a first approximation, it was assumed that they result exclusively from the hydrolysis of the elastically active chains constituted by the amidoamine hardener. Indeed, at low conversion ratios, the reaction of amides with water and the accumulation of dangling chains with highly polar extremities (carboxylic acids) in the epoxy network could explain the progressive increase in the equilibrium water mass uptake m_∞ over time. At highest conversions ratios, i.e. when the probability of having two hydrolysis events on a same elastically active chain cannot be ignored, the physical loss of short macromolecular fragments (of diacid type) from the epoxy network could then explain the decrease in m_∞ over time. Complementary physico-chemical analyses are in progress to check these assumptions.