New aspects of aging in epoxy networks. II. Hydrothermal aging

Abstract

An amine cured epoxy is prepared in two different network states for hydrothermal aging. The "lowcrosslinked" network has a considerable amount of residual reactive groups and a relatively high-molecular mobility. The low-crosslinked matrix contains high-crosslinked regions. In contrast, the "highly crosslinked" epoxy system has little reactive groups and a lower molecular mobility. Here, low-crosslinked regions are found in a highcrosslinked matrix. Hydrothermal loading for both networks is performed in demineralized water at temperatures below their glass transition. The water plasticizes both kinds of networks which remain in the glassy state, however. As a consequence, in the low-crosslinked epoxy, the increased molecular mobility promotes an ongoing curing reaction leading to the consumption of epoxy groups until an almost complete network has formed. As a new aging process, phase separation occurs in the highly crosslinked epoxy. The new phase is more mobile than the matrix because it has its own glass transition at a lower temperature. In addition, thermooxidative degradation is observed for both network states. Certainly, these chemical and structural changes in the epoxy networks should influence the performance of an adhesive joint, a coating, or a fiber-reinforced composite.

Accelerated ageing versus realistic ageing in aerospace composite materials. IV. Hot/wet ageing effects in a low temperature cure epoxy composite

“…Considerable discussion and disagreement has occurred on the types of molecular environment of adsorbed water (bonded and nonbonded) and the types of absorption kinetics (Fickian or non-Fickian). [21][22][23][24][25][26][27][28][29][30] In contrast, the bulk of the industry testing has relied on the mechanical and fatigue (microcracking) effects on composite samples and has often used quite extreme conditions to accelerate changes. For example, the use of full water immersion at 708C, 908C, or even boiling water is common.…”

Solvent-Promoted Self-Healing Epoxy Materials

“…Other work involving water and epoxy resins suggests that the solvent may plasticize an epoxy matrix to allow molecular mobility that promotes further curing reactions, which could apply to the present system where solvent penetrates through the material to cause further crosslinking. 30,31 Spectroscopic evidence and thermal data will be necessary to elucidate the healing mechanism and will be reported in due course. …”

Aging behavior of a hot‐cured epoxy system

“…The phase separation observed for this hot-cured epoxy system is very similar to the phase separation in the fully crosslinked epoxy made of DGEBA and DETA by curing at room temperature and subsequent postcuring at 120°C for 1 h. 13,14 Therefore, the phase separation could be a characteristic aging mechanism for a wider range of epoxy systems.…”

“…The article complements two similar studies on the aging behavior of a room-temperature-cured epoxy system. 13,14 …”