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bioplasticsMAGAZINE_1405

Basics Biobased Building

Basics Biobased Building Blocks C 2 C 3 C 4 C 6 C 10 MEG C 2 H 6 O 2 H O H H H H 3 C C C OH C C OH HO C OH H H H Lactic Acid C 3 H 6 O 3 1,3-PDO C 3 H 8 O 2 HO H C H H C H Ethylene C 2 H 4 H O H C C C C OH H O H Succinic Acid C 4 H 6 O 4 examples for building blocks HO H 2 N H H H H H H C C C C C C H H H H H H HMDA C 6 H 16 N 2 Sebacic Acid C 10 H 18 O 4 H H C HO C OH H H H H H H C C HO C C H H H H 1,4-BDO C 4 H 10 O 2 NH 2 H H H H O H H H H C C C C C C C C C C H H H H O H H H H OH OH Most plastics that are called bioplastics today are biobased, that means derived from plants or other renewable feedstock. The different kinds of biomass provide of course various options to obtain biobased building blocks, which can be used for polymerisation. However, sugars in general and especially glucose is a molecule which is applied to produce a large number of different useful monomers mainly via fermentation. Sugar cane is a well-known source for glucose, but also all starch containing plants such as wheat. Not to forget cellulose also consists of glucose units. Plants as castor oil plant, rapeseed, soy, palm, flax, sunflower and many more contain plant oils, many of which can be converted to biobased building blocks especially when long-chained molecules are of interest. In the following an overview on the most common already found in the market is given, but also materials that are yet to face a brighter future are examined. Sugarcane provides bioethanol via the fermentation of glucose with yeasts. Bioethanol is not only important for the biofuel industry but the base for the important biobased ethylene monomer. In the simplest way ethylene is polymerized to PE. Biobased polyethylene, marketed as Green PE is already well known and established in the market. The ethylene building block can, however, be further used to produce biobased polypropylene via metathesis reactions. Technically this can already be done, but until now it is not commercially feasible to produce PP that way. Another well established, partly biobased plastic, which depends on the ethylene building block, is PET (polyethylene terephthalate). In a follow up step monoethylene glycol (MEG) can be produced from biomass-derived ethylene, which can be considered as a C2 building block just as its precursor. The biobased MEG is used in Bio-PET30, a bioplastic, which consists of up to 30% from renewable content. The reason why PET cannot yet be fully produced biobased is the terephthalic acid building block, which is currently used in its fossil based version for the Bio- PET. As it is the case for several aromatic monomers in the biobased sector, research is not as much proceeded as e.g. for the aliphatic olefins or polyols. There are possibilities to produce terephthalic acid from biomass (e.g. via p-xylene produced from sugars), but it is currently not carried out in a large scale yet, nevertheless likely to become available in the next years. 50 bioplastics MAGAZINE [05/14] Vol. 9

Basics By: Constance Ißbrücker Environmental Affairs Manager European Bioplastics e.V. Berlin, Germany An alternative biobased building block, which can be considered as substitute for terephthalic acid is 2,5-furandicarboxylic acid or in short FDCA. This fivemembered ring is obtained by oxidation of hyroxymethylfurfural and methoxymethylfurfural, which can be derived by the dehydration of plant based sugars. FDCA forms together with the biobased MEG a new 100% biobased copolyester polyethylene furanoate (PEF). PEF is said to have a better barrier to oxygen, carbon dioxide and water and better mechanical properties compared to PET. First batches are supposed to be commercially available in 2016. Fermentation of glucose with certain bacteria results in lactic acid monomers. Lactic acid is used to produce polylactic acid (PLA) usually via a ring-opening polymerisation. Depending on the type of bacteria used, D- or L-lactic acid is obtained (right or left left-turning or, more precise: dextrorotatory or laevorotatory). This is important, as dependant on the stereoisomerism of the monomers and their share and arrangement in the polymer chain the properties of the PLA will differ. Another building block with three carbon atoms used for bioplastics is 1,3 - propanediol (PDO). Some years ago the only biotechnological way to produce PDO was by the fermentation of glycerine. However, DuPont has developed a modified microorganism to obtain a biobased PDO directly from glucose. The monomer is for example used together with terephthalic acid to produce PTT (Polytrimethylenterephthalate). Succinic acid, a C4 building block, can too be produced via a bacterial fermentation of carbohydrates such as starch. It is used to produce polybutylene succinate (PBS) a biodegradable polymer. The second component for this bioplastic is 1,4 - butanediol (BDO), which in turn can be produced from succinic acid by a catalytic conversion, and thus be biobased as well. Bio-BDO will further be a valuable building block to produce biobased PBT (polybutyleneterephthalate) and also PBAT (Poly(butylene adipate-co-terphthalate)), a biodegradable polymer, which is currently found in the market as a fossilbased version. PDO and BDO belong to the group of diols, which means these molecules have two hydroxyl (OH) groups. Generally, diols and molecules that have more than one hydroxyl group are called polyols. Polyols, however, can also be derived from oil plants such as castor, soy, canola, sunflower etc.. These usually long chain molecules can be used to produce PUR, more precisely partially biobased polyurethanes (PUR). The isocyanate component required to carry out the polymerisation to PUR can currently only be produced from fossil resources. Another polyol made from PDO as starting material is used to produce the thermoplastic elastomer Hytrel ® . Polyamides usually consist of dicarboxylic acids and diamines. Obtaining these both substance groups from biomass provides a large portfolio for the production biobased polyamides. Sebacic acid a C10 building block is already successfully produced from castor oil. With this monomer partially biobased polyamides as PA 4.10 or PA 6.10 are obtained and available in the market. 1,10 -Diaminodecane another C10 building block can be also produced from castor oil (via sebacic acid) and therefore a 100% biobased PA 10.10 is already available in the market. For a partially biobased PA10.12 the diaminodecane monomer can be used together with the fossil-based dodecanoic acid. However, also the C4 building block for polyamide is in principle available by derivatisation of succinic acid. For a C6 building block for polyamides adipic acid, which can also already be obtained from sugars is likely to become an important starting material. Via adiponitrile HDMA (hexamethylenediamine) can be produced, which will not only be the building block for PA 6.10 but for all other PA 6.X paving the way for biobased nylon. Aminoundecanoic acid a building block also made from castor beans is used to produce biobased PA 11, which is in fact not a bioplastic of the new generation but has been in the market for decades. Moreover, a route to obtain ω-amino lauric acid from palmoil has been recently developed to produce biobased PA 12. The possibilities for biobased monomers in general, but also as building blocks for the production of bioplastics seem endless. However, there are still biobased feedstock and routes for a numerous amount of substances yet to be discovered and research in this field is constantly increasing. Carbohydrate feedstock especially when it contains starch and sugars is already well investigated as well as possibilities oil-containing plants are carrying. When it comes to cellulose feedstock it is already well known that the polysaccharide is an alternative source for glucose. However, where cellulose is found there is also usually lignin. Lignin as a biopolymer consisting of a large variety of mainly phenolic and therefore aromatic monomers units is already used in the bioplastics sector but might also be as source for further building blocks in the near future. bioplastics MAGAZINE [05/14] Vol. 9 51

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