Deterioration of polyethylene pipes exposed to chlorinated water

Pipes of high-density polyethylene were exposed to chlorinated water at elevated temperatures. The materials were stabilised with hindered phenols and phosphites. Oxidation induction times measured by DSC showed that the stabilising system was rapidly chemically consumed by the action of chlorinated water. Size exclusion chromatography and DSC showed extensive polymer degradation strictly confined to the immediate surface of the unprotected inner wall material and to the amorphous phase of the semicrystalline polymer. The rate of growth of the layer of highly degraded polymer was constant. It is obvious from the data that the species responsible for the loss of antioxidant are soluble in the polymer but not very reactive with the polymer itself. The species responsible for polymer degradation, on the other hand, are very reactive with the polymer and/or have a very low solubility in the polymer. (C) 2004 Elsevier Ltd. All rights reserved.