Effect of aging in hot chlorinated water on the mechanical behavior of polypropylene grades differing in their stabilizer systems

Polymeric materials used in solar-thermal applications are exposed to superimposed mechanical (e.g., system pressure) and environmental (e.g., temperature and environmental medium) loads. The environmental loading induced degradation of the polymers leads to diminished mechanical properties and to the reduction of the product lifetime. This paper describes the characterization of the mechanical behavior (i.e., strain-at-break and essential work of fracture) of four different polypropylene (PP) grades immersed for up to 750 h in chlorinated water (5 ppm chlorine content) at 60°C. The strain-at-break values exhibited a similar exposure time dependence as the essential work of fracture values. Depending on the PP grade, time-to-embrittlement values of 375 h and 750 h were obtained. For the three different stabilized PP grades, both testing methods led to an equal time-to-embrittlement value of 750 h.