Time-carbonyl groups equivalence in the photooxidative ageing of virgin/recycled polymer blends

The photo-oxidation behaviour of polymers is strongly dependent on the initial amount of carbonyl ; groups along the chains. The growing use of recycled post-consumer polymers coming from products used outdoors and then photo-oxidised, both pure and blended with the same virgin polymer, gives rise to an unpredictable behaviour of weathering resistance of products made with these materials. The present work shows that the carbonyl group-exposure time curves can be shifted along the time axis to give a single generalised master plot. It is then possible to predict the formation of the new carbonyl groups by knowing only the initial amount of the same carbonyl groups. The same shift factor cannot be applied to quantitatively predict the changes in mechanical properties of the materials because these characteristics depend on other parameters. Nevertheless, this technique can give useful information on the decay of the mechanical properties.