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Duration of exposure (days)

Figure 10.2. Deterioration of enhanced photodegradable polyethylene film and control polyethylene film exposed floating in seawater in Biscayne Bay, Florida.

Duration of exposure (days)

Figure 10.2. Deterioration of enhanced photodegradable polyethylene film and control polyethylene film exposed floating in seawater in Biscayne Bay, Florida.

to the heat buildup resulting in higher sample temperatures for samples exposed in air. Several exposures carried out at a freshwater location also showed the enhanced-photodegradable plastics to function adequately in freshwater as well.4

Gradient B of a semilogarithmic plot of percent extensibility versus the duration of outdoor exposure of the sample provides a good measure of its rate of deterioration (see Table 10.6). Of particular interest is the ratio of BA, the gradient for the plastic samples exposed in air, to BN, that for the same sample exposed in the marine environment. This ratio of (BA/BN) > 1 obtained for these locations indicated the disintegration of the enhanced-photodegradable polyethylene samples exposed under marine conditions to be very much slower than for exposure in air; the samples exposed in air degraded at a rate of 50-400% faster. This is consistent with the earlier observation that the rate of photodegradation of plastics is relatively slower when the samples were exposed floating in seawater. While their performance was relatively slower in seawater, enhanced-photodegradable polyethylenes did function adequately under marine exposure conditions. The improvement in the rate of degradation is significant in that the photodegradable six-pack ring material embrittled within 5-10 weeks of marine exposure as opposed to years of exposure needed by the same product made out of regular polyethylene resin. Regular polyethylene samples of comparable dimensions

4 In most parts of the United States near the coast, the six-pack carriers are now required to be made with enhanced-photodegradable plastics materials.

exposed as control samples at the same locations and suffered minimal losses in extensibility within the period of observation. These latter samples are more likely to foul and sink to the benthic regions continuing to pose a threat to marine life, long before it is disintegrated. In terms of preventing entanglement-related damage and reducing the aesthetic problems associated with floating plastics debris, the enhanced-degradable technology provides a practical and valuable mitigation option.

Despite the encouraging results, it is important to point out that photodegrad-able plastics, while helping to ease entanglement-related impacts, do not offer a complete solution to the problem. Rapid disintegration of the plastic into smaller particles does little to alleviate (or can even increase) the risk of ingestion of plastics by marine birds and other species. While it can perhaps help prevent ingestion-related distress in the larger visible species (such as birds and turtles), the impact on the smaller animals (such as invertebrates, specially the filter feeders) must correspondingly increase.

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