Fig. 3 shows the dependence of molecular weight to the time (in years) as calculated from the time elapsed in the QUV test chamber. It can be concluded that the effect of ageing on the molec- ular weight of the previously reprocessed samples was similar in both cases. The molecular weight decreased very quickly from the beginning and remained practically constant after that. On the other hand, the molecular weight distribution underwent a slight increase (from 1.7 to 1.9) when the sample was subjected to an ageing process. This behaviour reveals the great degradative effect that the environmental conditions exert on the molecular weight of the samples, since from the first analyzed period an important