vor 7 Jahren

01 | 2008

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End of life Recycled

End of life Recycled bioplastic film Recycling of Bioplastics When talking about end-of-life options for bioplastics, composting is very often the first solution to be mentioned. And even with the increased discussion of incineration and energy recovery as being perhaps a better solution, we should not forget that re-use and recycling are end-of-life options, or steps in an end-of-life scenario that should be exploited wherever possible. And recycling of bioplastics materials is possible, albeit not always easy. bioplastics MAGAZINE spoke with Klaus Feichtinger, General Manager at EREMA Engineering Recycling Maschinen und Anlagen Ges.m.b.H. in Ansfelden, Austria. bM: Mr. Feichtinger, Erema is world renowned for its recycling technology for conventional thermoplastics. But what about bioplastics? Feichtinger: We have indeed extensive experience with bioplastics, both from laboratory tests and from real recycling tasks with customers. These include blown films, cast films and even BO (biaxially oriented) films made of modified starch, PLA, or fossil-based biodegradable polymers. We have tested, for example, quite a few different Mater-Bi films, Ecoflex films and different mixtures. bM: What kind of machinery was applied to carry out these recyling tasks? Klaus Feichtinger Feichtinger: Basically our existing machines can be used without modifications. However, temperature and pressure conditions have to be adapted to the requirements of the different materials. For films without printing we suggest the Classic Erema System with cutter/ compactor, and single screw extruder without degassing. bM: But many films used today are printed ... Feichtinger: For films with extensive printing a different degassing screw design has to be chosen. For good degassing a sufficient pressure gradient is needed. On the other hand the screw design has to meet the temperature requirements in order to to avoid thermal degradation. Also important in this respect is the type of pigment carrier used in the printing inks. Many known 20 bioplastics MAGAZINE [01/08] Vol. 3

End of life carriers need higher temperatures in the recycling step, so for better recyclability the choice of pigments also might be important. bM: What about the recycling of PLA? Feichtinger: In the field of PLA our current experience basically covers two applications. The first is BO-PLA (bioriented PLA films). The edge trim, where the stretching clips are attached to the film, is thick enough to be directly fed back into the extruder. The slitter waste (cut off the final film), however is very thin, so that it cannot be fed directly into an extruder. Here our Classic Erema can be applied. There is, for example, one big production line for BO-PLA in France which is a modified BO- PP line. The Classic Erema that was initially supplied for the BO-PP production was later slightly modified to process BO-PLA with adapted process parameters. bM: And the second field of PLA applications ... ? Feichtinger: ... is cast film, for instance for thermoforming applications such as blister or clamshell packaging, or drinking cups. At 150 to 1000 µm this film is rather thick. The in-house production waste that has to be recycled is, for example, startup-waste, slitter waste or scrap webs. This waste material, be it PP, PS, ... PLA or whatever is used, is usually ground and fed back into the extruder. Now the trend is generally towards thinner wall thickenesses. If these thinner films are reground the bulk density decreases and the variation in bulk density increases which makes it diffcult to feed it back into the extruder. This thin-walled secondary material should be regranulated in an intermediate step in order to increase the bulk density. bM: And what kind of equipment is used here? Feichtinger: Well, PLA as well as PET is hygroscopic, which means it absorbs moisture. If a single screw extruder is used for recycling, these materials have to be pre-dried and pre-crystallized, which is difficult for PLA with its low glass transition temperature. Drying needs a long time and the material becomes sticky. Recycling with a twin-srew extruder still needs predrying. Especially with lower wall thicknesses the twin screw process also becomes more and more difficult due to the bulk density. Our VACUREMA process however is ideal for the recycling of PET as well as PLA material. Great variations in bulk densitiy can be processed and, thanks to the applied vacuum, even without pre-drying and pre-crystallization. bM: I assume that everything you just said about cast film and thermoformed applications is also true for PLA bottles? Feichtinger: Today I don‘t even think about PLA bottles. Even in the range of a few ppm, PLA would contaminate the PET recycling stream. We are happy that PVC is almost ‘extinct’ - at least in Europe. And now PLA ... bM: But if one day enough PLA bottles can be collected ... Feichtinger: If once there are enough PLA bottles and these are collected totally separately, the same recycling technology as mentioned before could be applied to PLA bottles. But until a significant critical mass can be reached for an economical PLA recycling I have the greatest concerns about PLA bottles and their potential to contaminate the PET recycling stream. Maybe a different end-of-life option for PLA bottles should be used, such as composting where possible, or incineration with energy recovery. bM: Thank you very much, Mr. Feichtinger. VACUREMA bioplastics MAGAZINE [01/08] Vol. 3 21

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