vor 7 Jahren

01 | 2008

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End of life Biopolymers

End of life Biopolymers - a discussion Defining the problems Composting Incineration Land-fill Biopolymer product Bio-gases Recycling ??? Article contributed by Hans-Josef Endres, Department of Bio Process Engineering University of Applied Sciences and Arts, Hanover, Germany Andrea Siebert, Scientific assistant, Department of Bio-Process Engineering, University of Applied Sciences and Arts Hanover, Germany Ann-Sophie Kitzler, Quality assurance and control Achilles Papierveredelung Celle GmbH In recent years there has been a steadily increasing market demand for biopolymers as alternative packaging materials. In parallel with the volatile but also steadily increasing price of crude oil there is a growing environmental awareness among politicians and consumers. With the general trend towards organically grown food and the use of natural and organic ingredients in personal care products it is also important to be aware of the way these products are packaged, and of the consumer‘s desire for a totally ecologicallyfriendly product. However, for an objective evaluation of the ecological potential of biopolymer packaging materials there are points to consider other than the simple use of biogenous polymers and/or the energy expended in its manufacture. When developing a life cycle analysis the potential for ecologically-friendly disposal of the material is also a decisive factor. Until now it was always compostability that was uppermost in the mind when considering biopolymer packaging materials. However a certificate of compostability does not automatically mean ecologically and economically satisfactory disposal of the biopolymer or the products based upon it. The example of PLA bottles in the PET recycling stream shows how, in general, a different approach to the end-of-life options needs to be taken for biopolymers. In many cases technical questions, such as that of recycling, have still not been fully answered, or the infrastructure for disposal of biopolymers is still inadequate. Therefore in this article we shall carry out a fundamental review of the different technical end-of-life options for biopolymers. Using the situation in Germany as an example we will look at the legislative framework, where the possibilities for the disposal of biopolymers are still given only rudimentary consideration. Recycling When considering the different end-of-life options the first thing that springs to mind is classic recycling. 22 bioplastics MAGAZINE [01/08] Vol. 3

End of life on „End of Life“ options There is, however, limited experience available in the field of thermoplastic biopolymers. Nevertheless similar problems to those encountered in the recycling of conventional thermoplastic materials can be expected. Because of their generally lower thermo-mechanical and chemical resistance we can assume an increased level of ‘downcycling’. Polymers such as PLA, for example, during recycling, exhibit a clear molecular breakdown. Furthermore there is a lack of compatibility between different types of biopolymer, and in particular in combination with conventional polymers. Recent research points to a ‘contamination’ of established reclamation processes, such as the significant negative impact that small amounts of PLA have on the properties of PET recyclate when it finds its way into the recycling process. Composting An alternative to classic recycling (although only for suitably certified materials) is composting. Most certificates however cover only the suitability of the material for industrial composting. This cannot be compared to complete biodegradability in a home compost heap. This means that all the certified compostable biopolymers available up until now on the market, after thorough investigation, exhibit good primary and secondary breakdown under industrial composting conditions, but there is often a lack of suitable composting facilities and infrastructure. The need for a separate collection, sorting and transport system presents a logistical, economic and, principally, an ecological problem because of the additional energy that has to be expended in transportation, thus having a negative impact on the overall eco-balance of biopolymers. It follows that composting is a sensible option only where, in addition to the extra expense with no technical benefits, it also offers an additional functional advantage such as is offered by agricultural film (e.g. mulch film), which the farmer does not have to collect or dispose of after use. It is simply ploughed in. In Germany for example certified compostable biopolymers are given preferential treatment with respect to waste disposal taxes. Until 2012 they are exempt from the German packaging ordinance, which means a saving of about 1.5 Euros per kilogram in ‘Green Dot’ packaging waste taxes. On the other side, there is in Germany legislation approving the use of fertilisers ‘produced only from biologically degradable products from renewable resources and waste materials generated during their manufacture’. This currently means that most biopolymers, despite their certified compostabilty, cannot be put into an industrial composting plant because input is restricted to materials that are 100% bio-based. A modification of the relevant fertiliser legislation is currently under discussion but there is no concrete conclusion in sight. Incineration Incineration of biopolymers appears to be a much more reasonable option. In addition to the energy recovery there is the advantage that biopolymers are almost CO 2 neutral when they are burnt. During combustion a carbon atom produces exactly the same amount of CO 2 as during composting, but incineration has an added benefit, whereas composting mainly represents added expense. The ‘bio-compatible composition’ of biopolymers also means that they have less potential to produce noxious substances in the combustion gases. However it is important that the use of possibly unknown biopolymer additives is taken into due consideration, especially in view of the increased future development of biopolymer materials. However, at the moment we have almost no practical experience of the combustion behaviour of biopolymers, such as their calorific value, ash softening, emissions etc. It can however be assumed that with biopolymers the high heteroatom content, in particular oxygen in place of carbon, will lead to an optimised bioplastics MAGAZINE [01/08] Vol. 3 23

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