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bioplasticsMAGAZINE_1303

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bioplasticsMAGAZINE_1303

PLA Recycling 1 1 H 3 C

PLA Recycling 1 1 H 3 C O O O O CH 3 D-lactide 1 H 3 C O 2 O O L-lactide O CH 3 1 1’ H 3 C O 2’ O O Meso-lactide O CH 3 Solvent 1’ 1.75 1.70 1.65 2 2’ 1.60 1’ Figure 4 Proton NMR of the recovered lactide from PLA depolymerization 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm) recovery of lactide was unaffected when the amount of Ecoflex was lowered to below 25 wt% in both samples. The addition of resin SnO 2 catalyst to the blended samples seemed to lower the recovery of lactide by approximately 10%-15% in blends with greater than 25% Ecoflex. One possible explanation for the decreased lactide recovery in blended samples could be due to the transesterification reaction between PBAT and the lactide oligomers. The depolymerization rate of PLA at constant catalyst concentration is dependent on temperature following the Arrhenius equation The thermogravimetric analysis of samples with 0.6% catalyst at different temperatures are shown in Figure 5. At lower temperatures (160-180), the rate of the reaction was low. After 60 min, the weight loss was less than 50%. In contrast, at 210, the depolymerization reaction resulted in 100% weight loss within only 30 min. In summary, the authors have shown that PLA polymers and their blends can be recycled back to lactide in 95% yields by using a simple catalytic thermal depolymerization process with lactide recovery by distillation. Kinetic modeling and engineering parameters development is in progress to scale to a pilot plant. [1] Ramani Narayan, Biobased & Biodegradable Polymer Materials: Rationale, Drivers, and Technology Exemplars; ACS (an American Chemical Society publication) Symposium Ser. 1114, Chapter 2, pg 13-31, 2012 [2] Ramani Narayan, Carbon footprint of bioplastics using biocarbon content analysis and life cycle assessment, MRS (Materials Research Society) Bulletin, Vol 36 Issue 09, pg. 716 – 721, 201 [3] Witzke, D. R.; Narayan, R.; Kolstad, J. J., Reversible Kinetics and Thermodynamics of the Homopolymerization of l-Lactide with 2-Ethylhexanoic Acid Tin(II) Salt. Macromolecules 1997, 30 (23), 7075-7085. [4] Narayan, R.; Wu, W.-m.; Criddle, C. S., Lactide Production from Thermal Depolymerization of PLA with applications to Production of PLA or other bioproducts. US Patent 13/421780 3/15/2012 Weight percentage [%] 100 80 60 40 20 0 0 10 20 30 40 50 Time [min] Thermograms (TGA) of PLA depolymerization at different temperatures (from bottom to top: 210, 200, 190, 180, 170, and 160) at 0.6% catalyst concentration. 44 bioplastics MAGAZINE [03/13] Vol. 8

PLA Recycling Solvent based PLA recycling Fig. 2: no colour changes by Nathalie Widmann, Tanja Siebert, Andreas Mäurer, Martin Schlummer / Fraunhofer IVV Felix Ecker / University of Applied Sciences Fulda In many cases waste containing PLA is currently sorted out as an impurity during the disposal of plastic materials, since low PLA amounts do not yet justify recycling activities. Instead PLA, separated from post-consumer waste, is finally processed into refuse-derived fuel or in waste incineration. With the increasing quantities in recent years the necessity also increases to establish efficient recycling systems for PLA and generate high-quality recyclates guaranteeing a good resource-efficiency. However, recycling of PLA is challenging since in packaging materials PLA is often used as a composite or blend. The main issues are therefore the separation of pure PLA fractions from post-consumer waste and the preservation of its mechanical properties in order to obtain a high-quality recyclate. These issues have not been solved by mechanical state-of-the-art recycling technologies. The solvent-based CreaSolv ® process was developed by the Fraunhofer Institute for Process Engineering and Packaging IVV in Freising, Germany, in cooperation with the CreaCycle GmbH in Grevenbroich, Germany (owner of the trademark). It represents a future-oriented alternative for the recycling of PLA. The process has been developed for conventional thermoplastics (e.g. PET, ABS, PA, PP, PE and PS) and generates pure and high-quality polymer recyclates from contaminated and heterogeneous waste. The process can be divided into four main steps including solution, cleaning, precipitation (the formation of a solid in a solution during a chemical reaction) and drying of the polymer (Fig. 1). The CreaSolv formulations used are selective for the respective plastic and non hazardous. Furthermore the process involves precipitation stages for soluble contaminants like degradation products, oligomers or undesired additives. It returns a solution of purified macromolecules where the size and molecular weight were found to comply with virgin material. The major advantage of the CreaSolv process over established mechanical recycling processes is the ability to separate effectively both undissolved foreign polymers and non-plastic materials from the dissolved target plastics. It is therefore particularly suitable for mixed waste and composites. Initial studies on a laboratory scale with PLA allow first statements about solvent selection and selectivity. The PLA solvent was applied to other typical packaging materials (PE, PP, PET and PS) and was confirmed to be selective for PLA. First results show that the molecular weight of PLA can be maintained by specific process control during the dissolution, precipitation and drying stages. Also colour changes of the PLA can be avoided by certain conditions (Fig. 2). Currently, results from laboratory scale experiments are being transferred onto the small scale technical line at the pilot plant of the Fraunhofer Institute in Freising. www.ivv.fraunhofer.de www.creacycle.de solvent refining waste solution purification precipitation drying product impurities, contaminants Fig. 1: CreaSolv process (Source CreaCycle) bioplastics MAGAZINE [03/13] Vol. 8 45

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