Plastics and Environmental Sustainability by Anthony L. Andrady

Author:Anthony L. Andrady [Andrady, Anthony L.]
Language: eng
Format: epub, pdf
ISBN: 9781119009399
Publisher: Wiley
Published: 2015-03-16T00:00:00+00:00

Figure 6.8 Weathering of unstabilized LDPE films (open symbols) and enhanced photodegradable ECO copolymer (filled symbols) exposed outdoors in Miami, FL.

Table 6.2 Location-dependent Enhancement in Photodegradation Obtained Using ECO Copolymer in Place of LDPE Laminate of Same Thickness (Andrady et al., 1993a)

Location of exposure Degradable plastic ECO ( B × 103) days−1 Control plastic LDPE ( B × 103) days−1 B*/B

Cedar Knolls, NJ  52 9.5 5.5

Chicago, IL  87 4.3 20

Miami, FL  69 14 4.9

Seattle, WA  40 4.2 9.5

Whitman, AZ 257 25 10

6.3.1 Effects of Photodegradation on Biodegradation

Photo-oxidative degradation results in several changes in the polymer. Primarily, the average molecular weight Mn (g/mol) is reduced along with the mechanical integrity of the material. Also, it increases the surface hydrophilicity encouraging faster subsequent biofilm formation (Donlan, 2002), a prelude to potential biodegradation. Finally, any brittle fragmentation reduces particle size and therefore increases the specific surface area favoring faster biodegradation. It is interesting to study the change in Mn (g/mol) with the decreased extensibility, particularly at embrittlement when the plastic is reduced to small fragments.

In Figure 6.9, the average tensile extensibility, ε, is plotted versus the Mn (g/mol) of the plastics weathered to different extents as determined by GPC for polyethylene (LDPE) and ECO copolymer. Interestingly, even the completely embrittled material (ε<5%) is still a high polymer (Bates and Sidwell, 2006), with molecular weights far too high for any appreciable biodegradation to occur. Mineralization of common plastics with Mn (g/mol) > 103 (g/mol) has not been reported in the literature. It is sometimes suggested that extensive photo-degradation reduces Mn (g/mol) sufficiently to facilitate faster biodegradation. These findings are not consistent with such a claim.

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