Environmental Engineering Reference
In-Depth Information
Figure 6.3
The cyclic autoxidation reactions for a polyolefin RH.
6.2.1 Light-Initiated Photo-Oxidation in PE and PP
The mechanism of light-induced degradation in PE and PP is autocatalytic
oxidation of the polymer that is accompanied by main-chain scission (Singh
and Sharma, 2008; Balabán et al., 1969). Solar UVR initiates this reaction
by creating free radicals that propagate via a well-established cyclic
sequence of reactions. Thermal oxidation of these polymers also proceeds
via the same sequence of reactions but is slow at ambient temperatures.
It is, however, significant during high-temperature processing of plastics,
and thermal stabilizers are typically incorporated into plastics compounds
to avoid degradation during processing. Light stabilizers are used in
formulations intended for outdoor applications (such as siding, stadium
seating, mulch films, glazing, or rope). The basic autoxidation reaction
