Development and Implementation of an Accelerated Method for Chlorine Dioxide Exposure

In potable water distribution systems polyethylene (PE) pipes have been successfully used for several decades. In many applications chlorine disinfectants are frequently used to avoid harmful changes in the quality of water. Considering the intense oxidative ability of these substances, it is crucial to determine their influence on the degradation of pipe materials in long-term applications. At Polymer Competence Center Leoben GmbH (PCCL), a new device for material exposure under specific chlorine dioxide (ClO2) conditions was developed which allows significantly accelerated exposure of PE pipe materials. Preliminary tests were conducted in order to ensure stable exposure conditions during several weeks regarding temperature, pH value, ClO2 concentration and oxidative reduction potential (ORP) within a specified accuracy. Two PE grades for pipe applications were selected for conditioning and material testing. Dumbbell specimens of 1 mm thickness were punched out of compression molded sheets and fixed in an especially developed specimen holder made of chlorine resistant polytetrafluoroethylene (PTFE). The samples were exposed at 60 degrees C, 1 ppm of ClO2, pH of 6.8 resulting in an ORP of 550 mV and removed after 1, 2 and 3 weeks. Based on subsequent tensile tests, thermal analysis (DSC) and IR-spectroscopy (FTIR) a significant change in the mechanical properties as well as a thermo-oxidation was detected, emphasizing the effect of ClO2 on the physical and chemical aging of the materials even after one week of exposure. Optical surface investigation with scanning electron microscopy (SEM) confirmed the significant degradation of the materials revealing several micro cracks all over the specimen surfaces. The first results determined with the new exposure device show the potential of this technique for a tremendous reduction of testing time in order to study the degradation characteristics of polymeric materials under ClO2 exposure. Such information is of high importance to optimize the stabilization of polymers or to develop new stabilizers with improved effectivity.