Environmental Degradation and Durability of Epoxy‐Clay Nanocomposites

Abstract

This experimental investigation reports on the durability of epoxy-clay nanocomposites upon exposure to multiple environments. Nanocomposites are fabricated by mixing the clay particles using various combinations of mechanical mixing, high-shear dispersion, and ultrasonication. Clay morphology is characterized using X-ray diffraction and transmission electron microscopy. Specimens of both neat epoxy and the epoxy-clay nanocomposite are subjected to two environmental conditions: combined UV radiation and condensation on 3-hour repeat cycle and constant temperature-humidity, for a total exposure duration of 4770 hours. The presence of nanoscale clay inhibits moisture uptake, as demonstrated by exposure to constant temperature-humidity. Nonetheless, both materials lose mass under exposure to combined UV radiation and condensation due to the erosion of epoxy by a synergistic process. Surprisingly, the epoxy-clay specimens exhibit greater mass loss, as compared to neat epoxy. Mechanical testing shows that either environment does not significant affect the flexure modulus of either material. On the other hand, both materials undergo degradation in flexural strength when exposed to either environment. However, the epoxy-clay nanocomposite retains 37% more flexure strength than the neat epoxy after 4072 hours of exposure.

Environmental Degradation of Carbon Nanotube Hybrid Aerospace Composites

“…Furthermore, degradation phenomena due to UV radiation and moisture when acting together can significantly accelerate the degradation process of the matrix. Kumar et al (2002) studied the combined effect of UV and water vapor condensation and found that cyclic exposure leads to a synergistic degradation mechanism causing extensive matrix erosion and resulting loss of mechanical properties (Singh et al 2010). The combined exposure of UV radiation and condensation resulted in the loss of mass of both materials due to the erosion of EP by a synergistic physicochemical process that was previously identified and characterized by Kumar et al (2002).…”

“…It was therefore concluded that, nanoclay acted as a barrier and significantly hindered the moisture absorption of the EP matrix. The exposure to moisture did not result in significant changes of the flexure modulus, however, it led to degradation in flexural strength of both modified and unmodified systems with the modified ones being more resistant (Singh et al 2010). The combined UV radiation and condensation resulted in reduction of weight due to the erosion of EP with the EP-clay specimens showing higher deterioration.…”

“…Degradation is reported to occur for higher energy levels (wavelengths ranging from 280 to 400 nm). Since most polymers have bond dissociation energy .1 Temperature and relative humidity representative cycles reproduced after Reynolds and Mc Manus (2000) in the range of the wavelength of UV radiation (290-400 nm), they are affected greatly by exposure to the solar spectrum (Singh et al 2010). …”

“…They suggested the formation of photo-oxidative byproducts that underwent dissolution by water vapor condensation and run-off results in the removal of surface layers degraded by UV radiation. Therefore, cyclic exposure to both UV radiation and water vapor condensation results in a continual material degradation and erosion process (Singh et al 2010). Recently, Woo et al also suggested that the presence of moisture can enhance the mobility of free radicals and ions and, thereby, enhance the photo-oxidative effects of UV radiation (Woo et al 2007(Woo et al , 2008.…”

“…One interesting study is that of Singh et al (2010), which investigates the response of nanoclay modified EPs due to the combined effect of temperature-humidity and UV radiation. It was found that the presence of nanoscale clay inhibited moisture uptake, which was however lower compared to that of the unmodified system.…”