Environmental Engineering Reference
In-Depth Information
Figure 6.7
Simplified schematic of the mechanism of UV stabilization by
HALS. P refers to polymer chain.
Hindered phenols and quinone stabilizers also work via a similar
mechanism by removing free radicals from the system. Often, two or more
classes of stabilizers are used together to take advantage of synergistic
enhancement in stabilization (Gugumus, 2002b; Gugumus, 2002c). For
instance, combinations of two UV absorbers (an oxanilide with
benzophenone or benzotriazole or a phenylhydroxytriazine) were reported
to be systematically synergistic in both PE and PP. While most such
combinations are merely additive, some can even be antagonistic.
6.3 ENHANCED PHOTODEGRADABLE POLYOLEFINS
Plastics can be designed to photodegrade at rates that are several times
in agricultural films as they degrade and disintegrate into small pieces that
blend in with the soil at the end of the growing season, saving the expense of
removal of used mulch from the field for disposal. However, the long-term
impact of accumulating plastic (usually PE) fragments in the soil might be
unacceptable (Kitch, 2001). These are also used in the degradable six-pack
exposure outdoors within 6-8 weeks.
