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Materials Article

Materials Article contributed by Andrea Springer, Fraunhofer UMSICHT, Business Unit Renewable Resources, Oberhausen, Germany Polyamides Based on Biotechnological Succinic Acid The Fraunhofer research group develops innovative biobased polymers. The aim of one particular research group at Fraunhofer UMSICHT, funded by the German Agency for Renewable Resources (FNR), is the development of polymers based on renewable raw materials. The main targets of the project described in this article are polyesters and polyamides based on biotechnologically produced succinic acid. Background Polyamides are high-value polymers. Thanks to their excellent thermal and mechanical properties they are mainly used in special applications. The focus of the research group is the synthesis of polyamide 44 from the monomers succinic acid and 1,4-diaminobutane. The properties of polyamide 44 are expected to be similar to those of polyamide 46 which is already available on the market. Polyamide 46 is, as shown in fig. 1, a product in the mid price range which is primarily used in demanding applications. For polyamide 44 equivalent uses and similar or higher prices are expected. Thus it appears that industrial production of PA 44 can be competitive. From renewable raw material to the polymeric product Succinic acid is a dicarboxylic acid with a 4-carbon chain (fig 2). It is regarded as a favourable platform molecule in a sustainable chemical economy. Succinic acid can easily be produced from renewable resources by biotechnological high priced, special applications PEEK PTFE Figure 2: Chemical Structure of Succinic Acid (C 4 H 6 O 4 ) price low priced, commodity PP PS PET mid priced, technical applications PA 6 PBT PA 66 PA 46 PPS volume requirements Figure 1: Price ranges, production volumes and requirements of polymers 32 bioplastics MAGAZINE [04/09] Vol. 4

Materials Renewable resources Platform Fermentation Succinic acid Solvents THF g-Butyrolactone Dialkylsuccinates Monomers 1,4-Diaminobutane 1,4-Butanediol Intermediates Succinic acid anhydride Succinodintrile Polyester 44 Polyamide 44 Figure 3: From renewable raw materials to industrial end products synthesis, and there are different chemical pathways for the derivation of other important chemicals (see fig. 3) such as solvents, intermediates or monomers for the production of technical polymers. Presently, succinic acid is produced by a chemical process starting from crude oil via maleic acid anhydride. White biotechnology offers a good alternative to this petrochemical pathway. Succinic acid as an intermediate of the citric acid cycle and one of the end products of anaerobic metabolism can easily be produced via biotechnological processes. In the literature Anaerobiospirillum succiniciproducens, Actinobacillus succinogenes and Mannheimia succiniciproducens MBEL55E are mentioned as natural overproducers and potential candidates for industrial scale biotechnological succinic acid production. Handicaps of these micro-organisms are the expensive media, their slow growth and the low space/time yields. Worldwide research groups working on this subject pursue different ways to become competitive with the petrochemical route - mainly cost and yield optimisation as well as genetic modification of the micro-organisms. On account of the observable market fluctuations concerning volumes and prices the process under development needs to be operable with different renewable raw materials. Furthermore, cost reduction and yield increase by optimisation of the fermentation medium is being investigated. After the fermentative production downstream processes purify the succinic acid for the following steps: ‘chemical conversion‘ and ‘polymerisation‘. Chemical reactions convert succinic acid into technically relevant platform chemicals and into the monomers for polycondensation. The development of the synthesis routes takes into account the use of already existing petrochemical plants, so that no large investments are needed. Together with the products from its chemical conversion, especially 1,4-diaminobutane and 1,4-butandiole, succinic acid is used in polycondensation reactions leading to polyesters and polyamides. Their properties can be adapted according to market needs by copolymerisation. The overall process plant design should be suitable for large scale production. Expected properties and possible applications The expected properties of polyamide 44 will be similar to those of existing polyamides, which are characterised by good strength together with a high degree of hardness and stiffness. Furthermore, high abrasion resistance and dimensional stability are typical for polyamides. Estimates of the physical data of PA 44 can be extrapolated from those of polyamide 66 and PA 46. PA 44 will be characterised by an extremely high melting point and a very high crystallinity, but also by high moisture absorption. These qualities lead to the following three possible product groups: • Thermally and/or mechanically high resistant parts (preferably in water-free surroundings), for example oil-immersed gearbox or pump parts and other engine compartment units, soldering electrically resistant boxes and electronic components • Tear-proof fibres with high water absorption, e. g. for outdoor wear or textile adhesives • Hydrophilic and strong polymer membranes, e. g. for the use in filter technology bioplastics MAGAZINE [04/09] Vol. 4 33

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