Accelerated ageing method with chlorine dioxide. Application to additive free polyamide 66

With the aim to study the long-term behavior of accessories used in the tap domestic water supply system, the Centre scientifique et technique du bâtiment (CSTB) has developed a tool dedicated to accelerated ageing tests with chlorine dioxide in the experimental platform Aquasim. First studies performed with this tool show that this tap water disinfectant also attacks polymeric materials. Initially used for destroying micro-organisms, it is not totally selective since it also initiates oxidation radical chains in polymeric materials. This study is focused on additive free PA 66. Thin films samples were exposed to chlorine dioxide then characterized at different structural scales in the laboratory. One observes an oxidation and a sharp and extremely important decrease in the molar mass of PA 66 regardless the tested chlorine dioxide concentration. PA 66 embrittlement happens when the number average molar mass becomes lower than a critical value of about 17 ± 2 kg/mol. A kinetic model has been deduced from the mechanistic scheme of oxidation initiated by the radical attack of chlorine dioxide to predict, in a near future, the material lifetime. The model simulations match with experimental results