Environmental Engineering Reference
In-Depth Information
10.2.3.1 Comparison of the Weathering Rates in Different Zones
The difference in the rates of weathering is illustrated when the rate of
change in tensile extensibility of polypropylene sheets, exposed floating in
seawater in Biscayne Bay (FL) is compared to that on land at the same
location ( Fig. 10.1 ) . The figure also shows the marine exposure setup used,
consistingofaframewithfloats,thetestsamplesweretetheredto.Thesame
retardation of degradation is also seen with a range of different types of
plastics products commonly found in beach litter (Andrady, 2003; Andrady
and Pegram, 1989a, 1990a) as well as with enhanced photodegradable
plastics (such as the degradable six-pack rings). Consistently, the rate of
loss in tensile elongation (%) of samples was reported to be slower in
samples-exposed floating in seawater compared to those exposed in air. For
instance,thedecreaseintheaveragetensileextensibilityofplasticlaminates
exposed on the beach and floating in sea water for a period of 12 months
in Beaufort, NC, was as follows: low density polyethylene (LDPE) films
lost 95% in air and approximately 2% in seawater; PP tape lost 99% in
air but only 25% in the seawater exposure. Not only is the average tensile
elongation a particularly sensitive indicator of weathering or degradation
but it is also directly relevant to entanglement hazard posed by plastic
debris. Animals entangled in weathered and therefore weakened plastic
debris (e.g., netting) can free themselves with minimal harm.
 
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