Photooxidation and photostabilization of EVA and cross-linked EVA

Cross-linked EVA copolymers are widely used as encapsulant material for photovoltaic modules in order to protect the solar cell from the dangerous and degrading environmental factors like moisture and UV radiations. The protection of these modules from photooxidation is the main important objective in their production. In this work, samples of cured EVA in presence of different types of stabilizers have been photooxidized to better understand the photooxidation behavior and the effects of these stabilizers on the mechanical properties. All the results obtained on the cross-linked samples have been compared with those obtained in the same conditions and with the same formulations with the same uncured EVA. The photooxidation reactions are mainly due to chain-scission reactions with subsequent oxidation and decrease of the molecular weight and of the cross-linking density. The antioxidants are not able to protect the materials because are able to reduce the formation of oxidative species, but do not reduce the chain-scission reactions. On the contrary the HALS samples are able to strongly protect the cross-linked EVA because are able to contemporary reduce the formation and the reactions of the radicals and the oxidative reactions. By using these last stabilizers, the mechanical properties do not change significantly in the investigated long irradiation time range.