Prediction of degradation of polyolefins used in solar domestic hot water components

Solar Domestic Hot Water systems may include polymer components such as heat exchangers and absorbers. These components must be designed to consider heat transfer performance, mechanical (strength) performance and lifetime. Polymer degradation in potable hot water can be delayed through the use of antioxidant additives. In the present study, data are presented which show that antioxidant depletion in polyethylene (with a phenolic additive) is accelerated in potable hot water. Characteristic time scales are derived for this polymer/antioxidant combination at 80°C. These time scales indicate that the rate of antioxidant depletion is controlled by chlorine diffusion into the polymer (and subsequent reaction between the chlorine and antioxidant).