Ageing of polyethylene at raised temperature in contact with chlorinated sanitary hot water. Part I e Chemical aspects J. Castillo Montes a, b, * , D. Cadoux a , J. Creus b , S. Touzain b , E. Gaudichet-Maurin c , O. Correc a a Centre Scientiﬁque et Technique du Bâtiment Nantes,11 rue Henri Picherit, BP 82341, 44323 Nantes Cedex 03, France b Laboratoire d’Etude des Matériaux en Milieux Agressifs, EA3167 Université de La Rochelle, Avenue Michel Crépeau,17042 La Rochelle Cedex 1, France c Veolia Environnement Recherche et Innovation, Chemin de la Digue, B. P. 76, 78603 Maisons-Lafﬁtte Cedex, France article info Article history: Received 22 April 2011 Received in revised form 2 November 2011 Accepted 20 November 2011 Available online 26 November 2011 Keywords: Polyethylene raised temperature pipe Degradation Sodium hypochlorite Chlorinated water abstract In France, hot water quality control inside buildings is occasionally assured by disinfection treatments using sodium hypochlorite (between 0.5 and 1 ppm residual free chlorine). This disinfectant is a strong oxidizer and it could interact with metallic and polymer pipes used in hot water systems. To assess the long-term performance of these pipes, it is then necessary to study the impact of these treatments on the material behaviour, in particular for polymeric materials, even at relatively low disinfectant concentra- tions as used in potable water treatments. The objective of this work was to study the inﬂuence of sodium hypochlorite concentration on PERT/Al/PERT (PolyEthylene Raised Temperature) pipe degrada- tion. Pipe samples were ﬁlled with chlorinated water solutions (concentrations ranging between 0 and 100 ppm) and maintained in static conditions during 270 days at 70  C. The antioxidant depletion proﬁle through a PERT wall was monitored using the oxidation induction time (OIT) method, which is a conventional technique of Differential Scanning Calorimetry. Chemical changes on the aged polymer were checked by Infrared Spectrometry. OIT change showed that the PERT stabilizing system was rapidly chemically consumed by the action of chlorinated water at 25 and 100 ppm concentrations. However, PERT degradation was strictly conﬁned to the immediate inner wall. Only a 0.3 mm thick layer (inner part of the pipe) showed signiﬁcant antioxidant depletion. An increase of the OH and CeOeC infrared bands was also observed on inner part of any samples during ageing which characterize the oxidation of the PERT on the inner wall. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Normally, hot water distribution system temperature is main- tained at 50  C [1]; however, poor network dimensioning can create favourable conditions for microbiological growth (for example: Legionella). Disinfection is the most used process to control microbiological growth. In France, different types of products can be used to ensure disinfection, but the most widely used for treating hot water distribution systems is sodium hypochlorite (NaClO) between 0.5 and 1 ppm residual free chlorine [2] (1 ppm equals 1 mg/L). It must be noted that shock chlorination treatments are also used with a concentration up to 100 ppm without any pH control. Traditionally, metallic pipes (mainly copper and galvanized steel) have been used in hot water networks. These materials are, however, subject to corrosion, and disinfectants are relatively strong oxidizers which can accelerate corrosion [3e6]. As a result, in the past decades many polymeric-based materials have been used to replace these materials, mainly because of their “supposed” chemical inertia. Among these polymeric materials, polyethylene (PE) is frequently employed due to the fact that it is ﬂexible and has a high thermal conductivity [7]. High-density polyethylene (HDPE) is known to have good mechanical strength at elevated temperatures. However, the limited long-term creep characteristics of HDPE at high temperatures are unsuitable for hot water applications. Therefore polyethylene has to be modiﬁed to achieve the required thermo-mechanical proper- ties in hot water systems. Usually, cross-linked polyethylene (PEX) is used for hot water applications. Cross-linked polyethylenes are tough because their chains are bound together to form a network [8]. But, more recently, polyethylene molecular architecture has been adjusted (addition of octane co-monomers) in order to enhance the * Corresponding author. Centre Scientiﬁque et Technique du Bâtiment Nantes,11 rue Henri Picherit, CAPE, BP 82341, 44323 Nantes Cedex 03, France. Tel.: þ33 240376016; fax: þ33 240372040. E-mail address: jaime.castillo-montes@cstb.fr (J. Castillo Montes). Contents lists available at SciVerse ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab 0141-3910/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2011.11.007 Polymer Degradation and Stability 97 (2012) 149e157