Aging of Polyethylene Pipes Transporting Drinking Water Disinfected by Chlorine Dioxide. I. Chemical Aspects

Aging of unfilled polyethylene (PE) films in concentrated (80-100 ppm) chlorine dioxide (DOC) solutions at 20 degrees C and 40 has been studied by IR spectrophotometry, melt rheometry, chlorine titration, and tensile testing to establish the mechanisms of PE degradation induced by DOC, to determine some important kinetic parameters, to identify the embrittlement mechanism, and to examine the possibility to predict nonempirically embrittlement from a kinetic model. Experimental results reveal that DOC initiates PE oxidation. This latter is responsible for hydroperoxide build-up, and chain scissions occur when hydroperoxides reach a critical concentration above which they decompose bimolecularly. The weight average molar mass M-w decreases and embrittlement occurs when M-w approaches a value of 70 kg mol(-1) as previously found in thermooxidation studies. A mechanistic scheme involving all the elementary steps of PE autooxidation plus one initiation and one termination step involving DOC has been elaborated. The kinetic scheme derived from this mechanistic scheme has been solved numerically and the results of simulations have been compared with experimental results. POLYM. ENG. SCI., 49:1429-1437, 2009. (C) 2009 Society of Plastics Engineers