Polymères : protection par additifs

Protection of polymers by additives

Ciba - Geigy SA, Fribourg, Suisse

Abstract

Thermooxidation and photooxidalion of polymers and coating are currently inhibited in an efficient manner by antioxidants and photostabilizers. Although it is difficutt to distinguish these two types of degradations from a practical point of view they arc discussed here individually.

Thermally initiated degradation in the presence of oxygen (thermooxidation) may be slowed down or inhibited by chain-breaking (printary) antioxidants (i.e. sterically hindered phenols) and/or preventive (secondary) antioxidants (i.e. phosphites). Combinations of these two types of antioxidants may lead to synergistic effects.

Light induced degradation in the presence of oxygen (photooxidalion) may be prevented by different kinds of UV stabilizers : UV absorber s (i.e. 2-(2' -hydroxyphenyl)-benzotriazoles ). free radical scavengers (i.e. HALS = Hindered Amine Light Stabilizers) and quenchers (i.e. organic nickel complexes) just to mention the most commonly ised ones. Once again combinations of some of these photostabilizers may lead to even better resulls and even synergistic effects.

Besides such aspects as mechanisms and applications, the economical point of view is also discussed briefly.