Environmental Engineering Reference
In-Depth Information
Figure 6.12
Weight loss curves for PHB and PHBV (films and pellets)
incubated in tropical garden soil at two exposure sites in Russia: (a) Hoa
Lac and (b) Dam Bai.
Source: Reproduced with permission from Boyandin et al. (2013).
6.4.3 Testing Readily Biodegradable Plastics
Testing and quantifying polymer biodegradation is difficult because
simulated biotic environments are difficult to create in the laboratory in a
consistent manner. For instance, “compost” as used in D5338-92, “marine
sediment” in D6691-01, or “sewage sludge” as used in D5210-92 can have
very different microbial profiles depending on their source, and how they
were collected or cultured subsequently. Exposure of plastics to a
monoculture of specific microorganisms in the laboratory, followed by
visual evidence of colonization (ASTM G21-90 or G22-76) or CO
2
evolution
(D6691-01) can be carried out reproducibly but has little relevance to real
environments. Using “natural exposure” or field testing does not overcome
this difficulty because of their high degree of variability. This limitation
introduces significant variability into the standard test data on
biodegradation of plastics.
Andrady (2000) has reviewed the four common approaches available for
studying biodegradation of polymers. These involve experiments where one
of the reactants or a product is closely monitored. These are as follows:
