Photostabilization of Polymers

The photodegradation of polymers has been studied from the early years due to its commercial production. Most plastics are affected by exposure to sunlight in conjunction with other natural weathering forces such as oxygen, water, and heat. Almost all synthetic polymers require stabilization against adverse environmental effects. The consequences of photodegradation depend on the nature of the polymer and can cause polymer chain scission and cross-linking leading to changes at the molecular level. These irreversible processes eventually change the physical or visual properties of polymer to such extent that the end product cannot serve its purpose (Bolland and Gee 1946). It is necessary to find means to reduce or prevent damage induced by environmental components such as heat, light, or oxygen (Rabek and Ranby 1974a, b). The photostabilization of polymers may be achieved in many ways. The following stabilizing systems have been developed, which depend on the action of the stabilizer: (1) light screeners, (2) UV absorbers, (3) excited state quenchers, (4) peroxide decomposers, and (5) radical scavengers; of these, it is generally believed that excited state quenchers, peroxide decomposers, and radical scavengers are the most effective (Yousif et al. 2013). Research into degradation and aging of polymers is extremely intensive and new materials are being synthesized with a preprogrammed lifetime. New stabilizers are becoming commercially available although their mode of action is sometimes not thoroughly elucidated. They target the many possible ways of polymer degradation, thermolysis, thermooxidation, photolysis, photooxidation, radiolysis, etc. with the goal for increasing the lifetime of a particular polymeric material; two aspects of degradation are of particular importance: storage conditions and addition of appropriate stabilizers. A profound knowledge of degradation mechanisms is needed to achieve the goal (Yousif and Haddad 2013).