Towards a Non Empirical Kinetic Model for the Lifetime Prediction of Polyethylene Pipes Transporting Drinking Water

Abstract

Summary: A kinetic model has been elaborated to predict the lifetime of polyethylene pipes transporting slightly pressurized (3-12 bars) drinking water disinfected by free radical reagents. This model is composed of three levels: i) A system of differential equations, derived from a mechanistic scheme for radical chain oxidation in the presence of free radical reagents, giving access to the spatial distribution (in the pipe wall) of oxidation products and stabilizer concentration; ii) Equations allowing to predict the profiles of average molar masses from the spatial distribution of chain scissions and crosslinking events; iii) An empirical creep equation and a failure criterion derived from regression curves obtained in pure water (without disinfectant). It is assumed that the chemical degradation modifies only the time to transition between ductile and brittle regimes of failure, and that this time is linked to the weight average molar mass according to the classical power law. By superimposing these three levels, it is possible to predict the time to failure under the coupled effects of pressure and chemical degradation. This model is successfully applied to the case of chlorine dioxide.

Performance of PE pipes under extractive conditions: Effect of the additive package and processing

“…the diffusion of additives and oxygen, degradation reactions, etc. [5][6][7][8]. These processes depend on the polymer, the additive package, the surrounding environment and other conditions [9][10][11][12][13][14][15].…”

Degradation of Polymer & Elastomer Exposed to Chlorinated Water—A Review

“…For this purpose, it has been proposed that the chemical degradation induced by chlorine is responsible for the embrittlement mechanisms occurring at the inner surface [124]. In the case of polyethylene films, it is well known that polyethylene is brittle since Mw is below the critical molar mass (M'c) value; close to 40 kg·mol −1 [126]. More precisely, it has been Open Journal of Organic Polymer Materials…”

“…There are several ways to check the validity of the kinetic model. As an example, one can calculate the profiles in the pipe wall of [126]: -Antioxidants concentration (determined by differential calorimetry, assuming that the oxidation induction time (OIT) is directly proportional to the remaining antioxidants concentration [13] [112]; -Carbonyl groups build-up (determined by IR spectrophotometry); -Chlorine grafted to polymer (determined by elemental analysis); -Weight average molar masses (determined by rheometry in molten state);…”