Environmental Engineering Reference
In-Depth Information
Individuals may be tempted to choose an approach that gives a higher number,
perceived by the customer as 'better'. However, given the risks of 'green washing',
it is better for companies to report scientific, unambiguous information as DuPont
does in the example above.
Given that such ambiguity can arise, when considering the issues of environ-
mental impact a detailed life-cycle analysis (see Section 8.7) may be required to
better understand the situation in question.
8.6.2
Biodegradability
Biodegradability is an important parameter in some sections of the biopolymer sec-
tor but also where materials are exposed to the environment, for example lubricants
and greases. It is important to define what is meant by degradability in relation to
biobased materials, which can be different to that for fossil- or partially biobased
'biodegradable' polymers. In the latter case, additives can be incorporated into
materials such as PE, polypropylene, polystyrene and PET, accelerating the degra-
dation of the plastic in the environment. These additives (pro-oxidants) use a salt of
a transition metal such as cobalt, iron, manganese or nickel to drive the oxidation
process which, under the action of heat or light, will reduce the molecular weight
of the polymer to a level where bacteria and fungi in the soil environment can fur-
ther reduce the material into water and carbon dioxide. These products are known
as oxo-biodegradable, though the degradation process can take many months.
This has led to calls to differentiate between such materials by applying terms
such as 'biodegradable' only to those materials capable of being biologically
broken down completely (under specific conditions) in the absence of any other
stimulus, and 'degradation' to the breakdown of materials such as oxo-
biodegradable materials. Understandably this is an area of intense lobbying
between manufacturers in each camp, as manufacturers of oxo-degradable
polymers seek to be treated and recognised in the same way as other fully
biodegradable polymers. The outcome of such debates and lobbying is commer-
cially important and will affect the market share of any material that becomes
disadvantaged by widespread adoption of any particular standard definition.
A material can only be called biodegradable with respect to the specific
environmental conditions it is likely to encounter at the point of end-of-life
disposal, and by determination of the degree of degradation achieved over a
specific duration measured in those conditions (determined using a standard test
method). As a result of the potentially different end-of-life options available (e.g.
landfill, composting or anaerobic digestion) there are numerous standards
specifying the test methods for different applications or end-of-life scenarios. In
the UK for example these include [10] the following.
• BS EN ISO 14855-1 designed to simulate typical aerobic composting condi-
tions for plastics in the organic fraction of solid mixed municipal waste (see
also ASTM D5338).
