Environmental Engineering Reference
In-Depth Information
3.3.2.4 Photo-oxidative Degradation
Most of the synthetic polymers are susceptible to degradation initiated by visible and
UVlight.Normalsunlight(nearUVradiation290-400nm)determinestheoutdoor
lifetime of the polymer. The degradation mainly starts to occur from the ether part
of the soft segment. Photo-irradiation produces products including: aldehyde, ester,
formate and propyl end groups. The C−C bond can be cleaved if there is suficient
UV radiation [28]. The most speciic wavelength required to damage the polymeric
substance is dependent upon the bonds present in the polymer, for example, for PP
it is around 370 nm and for PE it is around 300 nm. Photo-degradation also changes
the physical and optical property of the polymers. The damaging effects include
yellowing, the loss of mechanical properties of the polymer, embrittlement, change
in MW and MWD [29].
Floating PE and PP ilms that are exposed to the solar UV radiation undergo a decrease
in their average MW, and loss of mechanical integrity, stability, extensibility and
strength. UV radiation in the 290-400 nm range has suficient energy for cleaving
most of the chemical bonds that result in the degradation of the polymer [30].
The photo-oxidation process is a radical based, auto-oxidation, which includes 4 stages:
initiation, chain propagation, chain branching and termination [31].
3.4 Biodegradation in Marine Environment
3.4.1 Presence of microorganisms (Bacteria)
Polymeric materials are the potential source of carbon for microorganisms.
There are two main ways in which microorganisms act on polymers: i) by the
deterioration of the plastics and then using it as a nutritive substance for their
growth and ii) by indirect action of the microbial metabolic products, e.g., further
deterioration or discoloration. Microorganisms cannot transport the material directly
through their outer cell membrane into the cells where most of the degradation process
occurs because of the length of the polymer molecules and lack of water solubility.
They excrete extracellular enzymes, which depolymerise the material outside the cells.
3.4.2 Nutrients
Magnesium, nitrogen, phosphorus and sulfur are essential nutrients for the degrading
microorganisms and plants or algae which grow in the marine environment. A polymer
