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UNUSUAL BEHAVIOR OF LIQUIDS, RESULTING FROM EXPOSURE TO POLYETHYLENE HARRY
C. GAT05
E. I. du Pout de Nemours & Company, Inc., Wilmington, Delawam
POLYETHYLEUE, a high molecular weight polymer, is a widely used plastic. Because of it,s chemical inertness, it has been recently employed in the form of containers for storage of chemicals such as mercury and inorganic acids. In connection with this application, several unusual effects have been observed. (1) After using mercury stored in polyethylene flasks for polarographic experiments, it was found that the polarographic maxima of Oz, Pb++, and Xi++ in 0.1 M KC1 supporting electrolyte were considerably suppressed. A very small decrease of the diffusion current was associated with the suppression of the maxima. Similar effects were observed by storing the 0.1 M KC1 supporting electrolyte in polyethylene flasks for about 15 hours and using mercury stored in ceramic containers. With this mercury the polarographic maxima are easily obtained under normal conditions. I t appears probable that surfaceactive constituents present in polyethylene are either mechanically removed or dissolved by mercury or the supporting electrolyte. They are possibly responsible for the suppression of the polarographic maxima. (2) It was found that the dissolution rate of SAE 1020 steel in dilute HC1 and H2S04is decreased in the presence of polyethylene. This is consistent with the concept that polarization phenomena involved in the suppression of polarographic maxima resemble the pollarization phenomena associated with corrosion inhibition in general.' In 10 per cent air-saturated HCI at room temperature the dissolution rate of st,eel was decreased by 40 to fiO per cent in the presence of fabricated (polyethI
GATOS.H. C., J. Elect~oehem.Soc., in press.
ylene flasks) or unfabricated polyethylene. The largest decrease of the dissolution rate (around 60 per cent) was observed in cases where the acid was in contact with polyethylene for various periods of time up to several months, prior to testing. The major portion of this effect was observed after only a few days of cont,act prior to testing. The acid in contact with the polyethylene was either dilute (10 per cent) or roncentrated and subsequently diluted to 10 per cent for testing. Similar effects were observed with nonaerated 10 per cent HCI. In 10 per cent H2S04-both air-saturated and nonaerated-the dissolut,ion rate of steel was decreased by 25 to 50 per cent. The lower values of rate d e crease were observed in rases where the acid was in contact with polyethylene for several months. This suggests a slow reaction between the active constituents in the polyethylene and sulfuric acid. The testing time for &eel dissolntion, for both HC1 and H2S04,was 1G hours. (3) The corrosion rate of 1020 steel in tap water at room temperature mas decreased by about 30 per rent in the presmoe of polyethylene in tests of 25 days' duration. The solubility of the polyethylene constituents responsible for the above reported effects is apparently very small since polyet,hylene flasks in use for as long as one year did not show any visual change. From the above it becomes apparent that although the chemical inertness of polyethylene is remarkable, care should be exercised when polyethylene equipment is being used in connection with polarographic and metal dissolution studies.
