All polymeric materials degrade under the influence of
heat, UV light and oxidation in general, which results in
the loss of mechanical properties and makes them brittle
(see section Degradation analysis below). Therefore, the
recyclability of plastics is limited to about six return cycles
under normal conditions, whereas it can drop to zero
when plastics are exposed to oxidative environments for
substantial periods of time.
9.1.1 Reco very options for waste plast ics
Plastics are complex materials for which the optimal way
of treatment after their useful service life is not always
obvious due to the combined influence of quality, raw
material prices and legislation. Few experts would argue
on the need and usefulness of recycling metals; however,
the question as to whether polymers from a given waste
source should be recycled as a material or whether the
energy should be recovered, is much more complex. The
main reason is that waste plastics can be used both as a
material and as a fuel, except for halogenated plastics,
such as PVC. In addition, plastics can be recycled as a
material a limited number of times due to degradation,
as outlined above.