Recent trends in the stabilisation of polymers

Polymers are subject to oxidation during processing due to the application of mechanical stress (shear) which leads to the scission of the polymer backbone and the formation of initiating macroalkyl radicals. Under the conditions of low oxygen concentration in commercial mixing operations, a catalytic redox antioxidant mechanism can operate which involves the alternating oxidation of alkyl radicals and reduction of alkylperoxyl radicals. ‘Stable’ free radicals (A) notably phenoxyl and nitroxyl radicals and inorganic radicals such as I are very effective melt stabilisers for polyolefins because of their ability to undergo reversible oxidation and reduction. magnified image A similar mechaism has been shown to operate during the mechano‐oxidation of rubbers in service (fatigue) and during the photo‐oxidation of polyolefins.