Stabilizer thickness profiles in polyethylene pipes transporting drinking water disinfected by bleach

Abstract

Polyethylene connection pipes of wall thickness ranging from 3.0 to 4.5 mm, used for 0, 5, 9, 12, and 18 years in the French network of drinking water disinfected by bleach, have been analyzed. The stabilizer thickness profiles reveal that bleach destroys the stabilizer in a superficial layer of about 0.5 mm depth at the water-polymer interface. In the rest of the wall, stabilizer is lost by physical processes, i.e., transport by diffusion into the bulk, extraction at the water-polymer interface, and evaporation at the polymer-air interface. The whole loss kinetics is governed by extraction and evaporation. The classical scheme for evaporation-diffusion process has been used to model physical loss processes, but with boundary conditions different from the literature ones. Concerning chemical aspects, some mechanisms proposed in the literature are criticized. The identification of the bleach reactive species remains an open question.