Ageing of Polyethylene Raised Temperature (PE-RT) in contact with Chlorinated Sanitary Hot Water

摘要

In France, hot water quality control inside buildings is occasionally assured by disinfection treatments using sodium hypochlorite. 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 concentrations as used in potable water treatments. The objective of this work is to study the influence of sodium hypochlorite concentration on PERT/AI/PERT (PolyEthylene Raised Temperature) pipe degradation. Pipe samples were filled with chlorinated water solutions (concentrations ranging between 0 and 100ppm) 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 (DSC). Chemical changes on the aged polymer were checked by Infrared Spectrometry (FT-IR). Mechanical property changes were assessed by tensile tests. OIT evolution showed that the PERT stabilising system was rapidly chemically consumed by the action of chlorinated water at 25 and 100ppm concentrations. However, PERT degradation was strictly confined to the immediate inner wall. Only a 0.3mm thick layer (inner part of the pipe) showed significant antioxidant depletion. An increase of the OH and C-O-C infrared bands was also observed on inner part of any samples during ageing which characterize the oxidation of the PERT on the inner wall. Tensile test results do not show effects of ageing on mechanical properties.