Synergistic effects of hygrothermal conditions and solar ultraviolet radiation on the properties of structural particulate-filled epoxy polymer coatings

Abstract

The synergistic effects of solar ultraviolet (UV) radiation, moisture, and in-service temperature on the properties of structural particulate-filled epoxy-based polymer coatings were investigated. The coatings contained up to 60% by volume of hydrated alumina powder and fly ash as fillers. Four sets of coating specimens (20 samples per set) with dimensions of 60 mm × 10 mm × 5 mm were prepared. Two sets were conditioned at a relative humidity of 98% and temperature of 60 °C for 2000 hrs (HG). One of these sets was then exposed to simulated UV conditions for 2000 hrs with the other set evaluated for the effect of HG conditioning. One set was unconditioned and served as control specimens with another set exposed to UV. Physical observations showed yellowing on the surface of neat epoxy coating after HG or UV exposure, but the presence of fillers minimized fading and weight loss. Regardless of conditioning environment, there was no reduction in the flexural strength for the polymer coatings containing at least 40% fillers. HG or UV exposure promoted post-curing, increased the glass transition temperature, and enhanced cross-linking density. Microscopic observation revealed the formation of surface microcracks after UV exposure that were wider with HG conditioning. ANOVA showed that the combination of HG and solar UV radiation negatively impacted the flexural properties of the coatings with up to 20% filler content but enhanced the coating properties with filler contents above 40%.