EFFECT OF CARBON-BLACK ON THE OXIDATION OF POLYOLEFINS - AN OVERVIEW

The use of carbon black in polyolefins is widespread. Two to three per cent of finely divided carbon black provides an effective light scree n protecting the polymer against exposure to light. In geotextile appl ications, use of carbon black is widespread due to demands for higher durability. Types of carbon black, their usage and interaction with th ermal antioxidants are reviewed. Current understanding of the effects of carbon black on the oxidation reaction shows conflicting evidence. Some workers have reported that carbon black accelerates oxidation due to surface catalysis of peroxide decomposition to form free radicals, adsorption of antioxidants from the polymer and increased accessibili ty of oxygen. Others have produced evidence of the inhibition of oxida tion by carbon black because of its activity as a radical scavenger an d its ability to decompose peroxides to form stable products. The role of reactive chemical groups on the carbon black surface, particle siz e and concentration are reviewed. It is evident that a full understand ing of the behaviour of carbon black in polyolefins is currently not a vailable and that it may depend on the balance of competing mechanisms of sensitisation and stabilisation in any specific formulation.