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bioplasticsMAGAZINE_1101

Materials Vegetable Oil

Materials Vegetable Oil Based Plastics – Produced Loss-Free A research group at the University of Konstanz, Germany, has developed a new approach to transforming fatty acids from vegetable oils into monomers for the production of thermoplastics. Prof. Dr. Stefan Mecking, chair of Chemical Material Science, explains the secret of the transformation like this: “Erucic acid and oleic acid both contain a reactive double bond in the centre. Previous polymerization methods using this bond produced branched materials with an irregular structure - barely useful for thermoplastics”. Alternatively, half of the molecule is “wasted” as a lateral chain. The development by his assistant Dorothee Qinzler now manages to make the whole molecule, loss-free, available as a monomer backbone: “Her method uses a catalytic method to let the double bond selectively shift to the end of the molecule where it is converted into an ester group. Now both molecule ends have reactive ester groups ready to be polymerized”. A characteristic of the new linear monomer is its ability to form plastics with a defined structure – in contrast to plastics made of erucic or oleic acid without any preliminary changes. The new material type shows high melting points and a good crystallinity and therefore it is well suited for thermoplastic processing. According to the scientists, the new polymer is best comparable to polyethylene regarding its crystal structure. The scale-up of the reaction should be technically quite feasible. Mecking says: “The reaction principles like carbonylation or polycondensation are already proven on a large industrial scale”. In addition the basic material that Quinzler uses is by no means exotic or purely academic: Erucic acid and oleic acid are two lowcost fatty acids available from a variety of sources, such as canola (rapeseed) or crambe. These plants can be grown in different climatic regions and therefore would be appropriate for a lot of different countries, especially for those with very limited access to raw materials such as crude oil or basic chemicals. Quinzler and Mecking do not regard plastics from renewable resources as a universal problem-solver for raw material supply. As Mecking states, even renewable resources are not available in unlimited quantity and quality but they do at least contribute to the total required raw material supply. “In the same manner that we do not use one single energy source, we won’t use one single raw materials source”, Mecking says. “We will always use a mix of resources, always using that resource which is best suited to the application”. He points out that plastics cover a wide range of applications and therefore a wide range of qualities – something one single type of plastic will never be able to provide. For that reason Mecking does not target specific applications for the new material yet. “Currently we are in contact with the industry for future use of the material indeed, but first we should carry out application trials to show for which application area the material has the best properties”. It is a realistic guess to say that the material is biodegradable and so this topic is a further focus for the team. The work in Konstanz has not ended yet. The group, grown in the meantime by three more assistants, wants to find out more about the new materials and their properties and wants to refine the catalytic step in the reaction in order to improve the yield. Even if some basic research is still needed, the current findings are very promising for future applications. BSL www.chemie.uni-konstanz.de/agmeck/ Reaction principle: The fatty acid ester (above) contains two reactive groups: An ester group (blue) and a double bond (green). Using carbon monoxide and methanol in the presence of a catalyst, the double bond shifts to the end of the molecule where it is transformed into an ester group. This molecule with two reactive ester groups (blue) now reacts to linear polymers. (source: University of Konstanz) X=1 or 5 ( ) x ( ) x COOR catalyst + CO + methanol ROOC COOR polymer 24 bioplastics MAGAZINE [01/11] Vol. 6

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