Accelerated hydrothermal aging of cycloaliphatic epoxy/graphene nanoparticle composites

Abstract

Cycloaliphatic epoxy (CE) resin systems are of primary interest in applications that require improved resistance to harsh conditions relative to other epoxy systems.Because other epoxy systems have demonstrated improved resistance to hydrothermal aging with the addition of carbon-based nanoparticle reinforcement, it is expected that the hydrothermal resistance of CE resins will likewise be improved with incorporation of nanoparticles. Therefore, the objective of this study is to determine the influence of graphene nanoparticles (GNP) on the hydrothermal aging resistance of CE resins. CE specimens are fabricated with varying levels of GNP and exposed to elevated temperatures and moisture levels for varying amounts of time up to 400 hours. The results from flexure and dynamical-mechanical testing indicate that the addition of GNP provides modest improvements in the stiffness and glass transition temperature for all aging levels, while the strength is improved for aging times below 400 hours.

Accelerated hygrothermal aging of Talc/Cycloaliphatic epoxy composites

“…Figures and show that the addition of talc increases flexural modulus for all aging times, from 3.2 GPa for the neat epoxy to 4.1 GPa for the 20 wt% talc/epoxy composite. This is expected for reinforcement in epoxy and for talc in polymers in general . The trend from these data indicates that higher talc content leads to higher flexural modulus, but other studies with similar filler and epoxy systems indicate that there may be an optimal amount of talc above 20 wt% after which the modulus decreases .…”

“…The final moisture content at 398 hr of aging was 3.2 wt% for the neat epoxy compared to 2.1 wt% for the 20 wt% talc composite. This is a dramatic improvement over previous aging research that used 2 and 4 wt% graphene nanoplatelets as a filler in a similar epoxy, where there were decreased moisture contents in the filled samples up to around 100 hr, but small/no differences at saturation . Starkova et al observed more significant impacts with thermally reduced graphene oxide (TRGO); water absorption decreased from about 5 wt% for unfilled epoxy to about 2 wt% for up to 0.5 wt% TRGO .…”

“…For all levels of talc, hygrothermal aging does not affect the flexural modulus. In a previous study with a similar epoxy system and the same aging procedure, flexural modulus decreased slightly for the neat epoxy and 2 wt% graphene after 200 hr of aging . There is not a similar drop in modulus with talc as the filler, which indicates that the talc/epoxy composite is more resistant to aging effects on modulus than graphene/epoxy.…”

“…Cycloaliphatic epoxies (CE) have shown greater resistance to many aging mechanisms relative to other epoxies, including hydrothermal, UV, and ozone aging mechanisms . This aging resistance is desirable for CE‐based composite materials used in outdoor applications or other harsh environments.…”

“…The effects of reinforcement on epoxy aging have been studied with various clay and graphene reinforcements . In general, these particles decrease the amount of water absorbed during hydrothermal or hygrothermal aging, which could decrease the effects of water on the mechanical properties of the epoxy matrix, and more specifically, the CE composite core of ACCC lines.…”