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06 | 2010

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Basics Recycling of

Basics Recycling of Bioplastics By Michael Thielen Initially it was planned to publish one comprehensive article on the recycling of bioplastics. However, it turned out to be a rather complex topic, so that now we will have this short overview about recycling of plastics and bioplastics and, in addition, a couple more specialized articles on recycling topics, including our cover story. Now, what does Wikipedia say about plastic recycling in general? “Plastic recycling is the process of recovering scrap or waste plastics and reprocessing the material into useful products, sometimes completely different in form from their original state. For instance, this could mean melting down soft drink bottles and then casting them as plastic chairs and tables.” I would like to differentiate this a little. First of all one can distinguish between A) clean production waste, B) post industrial waste or C) post consumer waste (also sometimes referred to as PCS = post consumer scrap). [1] Personal information, Klaus Feichtinger, Erema Engineering Recycling Maschinen und Anlagen Ges.m.b.H., Ansfelden, Linz, Austria [2] [3] [4] Different Sorts of Plastic Waste The recycling of production waste (A) is rather easy (and the article on recycling of bioplastics production waste on the following pages gives a more detailed picture). The recycling of sprues and runners in injection moulding, flashes in blow moulding or skeletons in thermoforming as well as waste parts from the startup of a process has been done in-line or off-line for decades. This material is mono-fractional (i.e. exact the same material) and can thus be fed into the process without contamination and up to a certain percentage without loss in quality. This applies to conventional as well as to bioplastics. Some requirements of bioplastics concerning recycling are the need for compacting (e.g. in case of very lightweight film or fibre waste), a pre-drying step (in case of hygroscopic materials such as PLA) and a crystallization step for amorphous materials such as PLA film waste [1]. Also in some cases a degassing and a meltfiltration might be necessary. The postindustrial waste category (B) comprises more different kinds of plastic waste. Here for example huge amounts of film material are being collected. Specialized companies buy baled film or bottles and recycle this material after some more or less sophisticated sorting processes. The secondary materials can be 50 bioplastics MAGAZINE [06/10] Vol. 6

sold at a certain sales price, depending on the quality, and can be used for instance for film blowing of waste bags, or in the middle layer of 3-layer blow-moulded parts. A more detailed description would be too much for this article (my apologies to the recycling industry). As long as significant amounts are being collected this can be an economic effort. For bioplastics this also seems a feasible option, as soon as a critical mass is reached for economic processes. Galactic in Belgium (see article on page 16) or BioCor in California, USA, for example started to buy back PLA in order to recycle it. The most difficult fraction of waste is post consumer scrap (C). The Recycling Network, Inc. from Sunrise, Florida, USA published on their website [2]: “Post-consumer plastic recovery on an individual basis is truly a volunteer effort, and generally does not generate profit from its collection and sale.” Again, recycling seems only feasible when a critical mass can be generated and when manual or automatic sorting as well as washing can be performed in an economical way. In Germany for example, where a lot of PCS is collected in the yellow bags or bins, a significant amount of bottles and film material is being recycled. With regard to bioplastics, one more factor makes recycling difficult: To make sorting and thus recycling basically easier, the American Society of Plastics Industry developed a standard marking code to help consumers identify and sort the main types of plastic. These types are [3]: PET PVC PP OTHER HDPE LDPE Here you see the problem for bioplastics… they are all under number 7 (OTHER). PS Different Recycling Methods Mechanical recycling of plastics refers to processes which involve the sorting, cleaning, and shredding, plus in some cases, also the melting and granulation of waste plastics. The shredded flakes or the granules can then be mixed with virgin material or converted into new products. Depending on the quality of the recyclate, the new applications can be of a lower quality, of the same quality (in cases even the same products such as bottle-to-bottle recycling) or used for totally different applications. The Recycled Products Guide (RPG) is a listing of products made from recycled plastic [3]. This website gives an example: It takes 25 x 2 litre plastic drinks bottles to make one fleece garment (one polyester application leading to a completely different one). Plastics must be sorted prior to mechanical recycling. At the moment in many countries most sorting for mechanical recycling is done by trained staff who manually sort the plastics into polymer type and/or colour. Technology is being introduced to sort plastics automatically, using various techniques such as X-ray fluorescence, infrared and near infrared spectroscopy, electrostatics and flotation. Following sorting, the plastic is either melted down directly and moulded into a new shape, or melted down after being shredded into flakes and then processed into granules called regranulate [3]. Some of these sorting techniques using, for instance, near infrared spectroscopy or laser technology, are also suitable to sort bioplastics such as PLA from a PET recycling stream (see bM 04/2009). Chemical or feedstock recycling describes a range of plastic recovery techniques, which break down polymers into their constituent monomers, which in turn can then be used again in refineries, or petrochemical and chemical production. A range of feedstock recycling technologies is currently being explored. These include: pyrolysis, hydrogenation, gasification and thermal cracking. Feedstock recycling has a greater flexibility over composition and is more tolerant to impurities than mechanical recycling, although it is capital intensive and requires very large quantities of used plastic for reprocessing to be economically viable (e.g. 50,000 tonnes per year) [3]. The chemical recycling of PLA is already being done for example by Galactic in Belgium (see p. 16) or BioCor, USA. Conclusion After ‘Reduce’ and ‘Re-use’ and before composting, anaerobic digestion or incineration with energy recovery (sometimes referred to as ‘thermal’ or ‘energy’ recycling) the ‘Recycling’ of bioplastics is an option that should be considered, provided that the material is either ‘clean and pure’ (production waste) or critical masses are available for economic commercial recycling. bioplastics MAGAZINE [06/10] Vol. 6 51

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