Accelerated photochemical ageing

This oxidation mechanism is called a close-loop mechanism , as it produces its own initiator product (Per). The resulting kinetic curves present an induction period followed by a sharp auto-acceleration, preceding a steady state. The auto-acceleration step is much more progressive in its initial phase when Per decomposition is unimolecular (the case for many photochemical ageings) (see Fig. 12.23). 

These findings clearly illustrate how the results of so-called "accelerated-aging" tests can be affected by the high temperatures in ordinary xenon- and carbon-arc equipment and can, therefore, lead to erroneous conclusions regarding the photochemical behavior of materials at near-normal temperatures (23). 

R.L. Feller, Accelerated Aging, Photochemical and Thermal Aspects, The Getty Conservation Institute, Los Angeles, 1994. 

A detailed long-term study of the photochemical behaviour of 95 (R = H) revealed that after several thousands of hours of accelerated ageing, surface deterioration becomes noticeable [342]. This deterioration was due to some photochemical oxidation of the methyl methacrylate units. The benzotriazole chromophore moiety remained unchanged. 

Recently, La Mantia et al reported a study of LLDPE/clay nanocomposites with appropriate additives [103], The photochemical behavior of nanocomposites without and with different UV stabilizers was studied under artificial accelerated conditions of ageing. Addition of a metal deactivator to the LLDPE-clay nanocomposites was also compared. Stabilizing effect on the physical properties such as elongation at break and tensile strength were described. The most effective photostabilization of these LLDPE/clay nanocomposites was achieved in presence of the metal deactivator. 

The photochemical deterioration processes of polymeric materials often used as paints and finishes are studied both theoretically and experimentally. Theoretical models for the deterioration processes are developed based upon unsteady state dynamics. The results were compared with experimental data under outdoor and accelerated aging... 

Feller, R. L. (1994). Accelerated aging Photochemical and thermal aspects. Getty. 

Feller RL (1994) Accelerated aging - photochemical and thermal aspects, p. 97... 

It is important to predict the aging effects of photochemical exposure on properties of materials before their use in different applications. In many applications, mostly ones occurring in the natural environment, exposure to UV irradiation must be taken into account at certain elevated test temperatures as means of accelerated... 

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