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The photodegradation of polymers poses a serious challenge to their outdoor application, and results in significant financial loss due to early or unexpected system failure. A better understanding of their degradation kinetics aids the improvement of materials and systems, however, most work to date on many polymeric materials focuses on only one or a few exposure conditions which are pertinent to typical environmental ambients. Here the model polyolefin system of high-density polyethylene (HDPE) was exposed under controlled laboratory conditions to a range of temperatures (30 °C, 40 °C, 50 °C) and ultraviolet (UV) light intensities (153 W m-2, 61 W m-2, 38 W m-2, 15 W m-2, 8 W m-2, and 0 W m-2). Changes to the mechanical, chemical, and structural properties were monitored by uniaxial tensile testing and Fourier-transform infrared spectroscopy (FTIR). The rapid embrittlement of HDPE was concurrent with increases in yield strength, stiffness, oxidation, and crystallinity, and the rate of change tended to increase under more aggressive exposure conditions. The photothermal activation energies and UV dose-damage relationships for these properties was determined, and indicate a similar underlying mechanism between loss of elongation-at-break and crystallization. A comparison to HDPE under outdoor exposure (southern Florida) shows a similar magnitude of material change up to the point of embrittlement, in spite of the much more varied outdoor conditions. These results quantify the effect of temperature and UV light intensity on the photodegradation of HDPE, and can be utilized to develop degradation mitigation strategies for these and related thermoplastic materials.
Polymer Degradation and Stability
HDPE, polymer degradation, accelerated weathering, kinetics, reciprocity, SPHERE