Antioxidants: hindered phenols

Abstract

Monohydric phenols differing in steric hindrance of the phenolic moiety and in their character of substitution at position 4 are typical chain-breaking antioxidants for commodity and engineering plastics. They have been used as processing stabilizers at temperatures up to 300°C, e.g. in polyolefins. In processing stabilization, they have been mostly combined with hydrolysis-resistant phosphites (secondary antioxidants). Long-term stabilization of plastics is the other principal application area. In this case, phenols are combined with photoantioxidants (hindered amine stabilizers, HAS) and UV absorbers (light stabilizers). The concentration level of phenols added to plastics is generally between 250 and 3000 ppm, depending on the character and expected lifetime of the polymer substrate [1]. Similar concentration levels of phenolics are used for the restabilization of recycled plastics. Permitted levels are administratively regulated for plastics in contact with food. Some suppliers of phenolic antioxidants are listed in Table 1.