New aspects of aging in epoxy networks. I. Thermal aging

Abstract

ABSTRACT:The thermal aging of an amine-cured epoxy in the glassy state is studied for two network states by using DSC and attenuated total reflection-infrared (IR-ATR). The "low-crosslinked" network possesses a relatively high molecular mobility and a considerable amount of residual reactive groups. In the low crosslinked matrix, the presence of high crosslinked regions is revealed. In contrast, the "highly crosslinked" epoxy system has a reduced molecular mobility and only small reactive groups. The high crosslinked matrix contains low crosslinked regions. Thermal loading for both networks is performed below their glass transition. During thermal aging, an ongoing curing reaction takes place in the low-crosslinked epoxy. Thermooxidative degradation and the disintegration of short-range ordering are observed as well. The highly crosslinked epoxy system undergoes a phase separation of relatively mobile segments in the low mobile matrix, which is a reversible process on heating. Thermooxidative degradation is also detected for this kind of network. In summary, for the "low" and the "highly" crosslinked epoxy, significant chemical and structural changes take place during thermal aging even though the networks are vitrified. It is convincing that these changes in the cured epoxy should exert an influence on the mechanical properties of a bonded structure.

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 corresponding T g is lower than the maximum glass transition temperature T gϱ,ideal that can be achieved by T c Ͼ T gϱ,ideal for the given epoxy system. 13,22,23 The following aging mechanisms are reported for epoxy systems. When a glassy network is annealed close to its T g in dry conditions, an endothermic enthalpy peak appears on the high-temperature end of the glass transition.…”

“…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 …”

Effect of Ultraviolet Absorber on Photo-Degradation of Epoxy Coating Studied by Slow Positron Beam

“…Polar groups can inhibit the formation of Ps and thus make the S parameter decrease [12][13][14]. In addition, during the initial stage of degradation, there exists a post curing process in the network of epoxy coating, which leads to a better crosslinked structure [15,16]. The reduction of free volume can also induce the decrease of S parameter.…”