Combined impact of UV radiation and nitric acid on HDPE containers during outdoor exposure

Unpigmented HDPE jerrycans filled with nitric acid (55 wt.-%) and water respectively had been exposed to outdoor conditions for one Berlin summer season. As both liquids underwent equal temperature progression, exposure effects of UV radiation and nitric acid as well as of the combination of both can be separated and compared. On the basis of various property changes after these exposures, synergistic action is evaluated and compared to a damaged Intermediate Bulk Container (IBC) from a transport accident. It is found that carbonyl formation accompanies lightness increase in color measurement due to microcracking and with a worsening in mechanical behavior, all of them showing the synergistic effects of UV and nitric acid exposure. By contrast, embedding nitrogen compounds accompanies yellowing of the material but cannot be correlated to oxidation. The reason for intensified damaging is the decomposition of the 55-percent nitric acid and the formation of nitrogen oxides even at ambient temperatures, caused by UV radiation. Thus, damaging effects become similar to those caused by fuming nitric acid exposure at temperatures above 60 degrees C, resulting in strong oxidative degradation of the polyethylene. By contrast, exclusive exposure to the 55 wt.-% nitric acid at 40 degrees C does not cause any failure. It can therefore be assumed that the damaged IBC too had been exposed to both UV radiation and nitric acid, probably outdoors.