vor 7 Jahren

01 | 2008

  • Text
  • Packaging
  • Bioplastics
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  • Recycling
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  • Germany
  • Compostable
  • Biopolymers
  • Polyols

End of life • The

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

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, bioplastics MAGAZINE [01/08] Vol. 3 25

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