01 | 2008

End of life
• The redistribution or conversion of
matter (mixing, wear, emission, waste…)
as well as the energy created, are taken
into account when considering entropy
generation over a full life-cycle.
• Entropy efficiency
= benefits obtained/entropy production
Information
Primary raw materials
(Plants, iron ore, petroleum)
Energy, sources of energy
(water power, petroleum)
CO 2
=
Benefits
E
Σ ΔS i
i=A
• The higher the entropy efficiency
the higher the sustainability
Raw material
(iron, ethylene,
cellulose, starch,...)
A
Pyrolysis
Recycling
Incineration
E
Waste, Scrap
Composting
Land fill
Production material
(steel, plastics,
ceramics)
W
Manufacturing
(buildings, machines,
components, packaging,
products)
K
V
G
Consumption
Wear, Failure
reaction rate of combustion but at the same time to a
reduction in calorific value similar to that seen in petrochemical
plastics. The calorific value will however
probably be well above that of wood and below that of
petroleum.
In this way biopolymers can also partially substitute
biofuels after their ‘first life’ and create a higher added
value from agriculture raw materials.
Bio-gas production
Until now there has been almost no consideration
of the production of biogas as a way of disposing of
biopolymers. Based on the fact that a normal biogas
plant produces gas in several stages under anaerobic
conditions using organic substrates, an efficient
biogas production from compostable biopolymers
seems quite possible. Alongside the energy reclamation
when the biogas is burned there is the added advantage
of joint disposal of the packaging and its food
contents. Any food products that have passed their
expiry date, rejects, or excess production, can be processed
together with their packaging and without the
expense of mechanical separation. But once again no
real practical figures have been obtained regarding
the conversion of compostable biopolymers in a biogas
plant (e.g. temperature, pH value, micro-organisms
present, degradation behaviour under anaerobic,
aquatic conditions…) or the relevant process parameters
(e.g. density of material flow, dwell time, gas
composition or yield).
In Germany the production of biogas and its subsequent
conversion to electrical energy is supported by
the so-called Renewable Energy Act (EEG). If, alongside
farmyard slurry, only materials coming from renewable
resources are used as a co-substrate the producer
receives an additional bonus of about 6 Euro Cents per
kWh of electrical power produced from the biogas. In
addition to investigating the technical feasibility of using
biopolymers it will also be necessary to ascertain
how, in the future, biopolymers containing varying levels
of renewable resources will be assessed.
Land-fill
Finally, the last of the disposal options, i.e. ‘simple’
dumping in a landfill site, must be considered. Following
the latest waste disposal legislation in Germany
household waste may only be deposited in a landfill
site when the percentage of dry organic substances is
less than 5% by weight. In addition the biological activity
in a land-fill site which produces environmentally
damaging gases by anaerobic decomposition, including
that from biopolymers, is a negative factor. It is,
depending on the landfill structure, possible to render
the methane gas harmless by burning it, and to use
the energy so generated, but the longer the dwell time
in the dump the lower the methane content becomes
and so this is an economical solution only in the early
stages.
24 bioplastics MAGAZINE [01/08] Vol. 3