Ultraviolet radiation polymer coating stabilization

Ultraviolet radiation is the other main stress encountered by polymers in the coatings arena. One hundred percent acrylic polymers are highly resistant to photodegradation because they are transparent to the vast majority of the solar spectrum (59). When uv-absorbing monomers, such as styrene, are incorporated into the polymer backbone, the uv-resistance of the resulting polymer decreases dramatically and a more rapid deterioration in polymer/coating properties is observed. On the other hand, a noncovalently bound uv absorber, such as hydroxybenzophenone [117-99-7], further improves the uv stability of 100% acrylic polymers (59). 

Solar radiation tends to degrade the performance of organic coatings and plastics, and stimulates biological formation and photosensitive electrochemical/corrosion reactions on copper or iron. Ultraviolet radiation can embrittle polymers unless UV stabilizers are added [fO]. 

The polymers made from 1,1-difluoroethene (or vinylidene fluoride) are known as polyvinylidene fluoride (PVDF). They are resistant to oils and fats, water and steam, and gas and odors, making them of particular value for the food industry. PVDF is known for its exceptional chemical stability and excellent resistance to ultraviolet radiation. It is used chiefly in the production and coating of equipment used in aggressive environments, and where high levels of mechanical and thermal resistance are required. It has also been used in architectural applications as a coating on metal siding where it provides exceptional resistance to environmental exposure. The chemical structure of PVDF is shown in Fig. 11.40. Some products are copolymers. 

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