01 | 2008

End of life
The outlook
In an ecological evaluation of the different end-oflife
options the most sustainable solution should be
the most favourable from an ecological point of view.
Because not only the energy expended during material
manufacture and during its use must be considered,
but also the redistribution and/or conversion of matter,
in particular during disposal, the scientific concept
of entropy efficiency may be used to determine the
sustainability of a material, product or process.
The use of fossil resources for energy production
and as industrial raw materials inevitably leads to a redistribution
or conversion of matter and a devaluation
of the resources of our planet, with less and less useful
forms of energy or materials being available. Only
in this way can we explain how on the one hand we
complain about global warming and the greenhouse
effect, and on the other hand we have an energy supply
problem. We cannot really make use of the heat energy
building up in the atmosphere.
Put simply, entropy is the measure of the irreversibility
of a product or process. That means that only in
ideal, totally reversible processes is no entropy generated.
In reality a certain entropy is generated by every
conversion process.
Thus, maximum sustainability of a product or process
means the lowest possible entropy generation over
the total life cycle, together with maximum benefit to
the user.
By using natural synthesis less energy is often used
for the production of biopolymers than for conventional
plastics. Biopolymers however not only have higher
entropy efficiency on the input side: by optimising the
disposal process their entropy efficiency can be further
enhanced. An example may be when a compostable
waste disposal bag or a resorbable implant offers
an additional benefit after its principal use, or when,
after reuse and/or recycling, the material is incinerated
to produce CO 2 -neutral energy. On the other hand
automatic recourse to composting or land-fill does often
not lead to benefit cascading but only to additional
expenditure, i.e. additional entropy generation without
benefit.
Biopolymers, because of the use of bio-based raw
materials, have a higher sustainability than conventional
polymers not only on the raw material side but
even at the end of their life through intelligent application
of the various disposal options. In conclusion
we can therefore reasonably assume that biopolymers
will represent a new class of materials in a plastics
market that is demanding ever more sustainability, in
particular with regard to future applications.
Entropy
Greenhouse
effect
CO 2
Heat
Combustion
of
petrochemicals
Emission
of CO 2
A B C D E F G H
Irreversible
enhancement
of entropy
Processes
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bioplastics MAGAZINE [01/08] Vol. 3 25