Castor oil, an important
Castor oil, an important source for bioplastics Fig 1: Castor seeds by Michael Thielen A number of biobased plastics, for example several partly or fully biobased polyamides are manufactured using sebacic acid as a monomer or as a chemical building block. Castor oil is the raw material of choice for the production of bio-based sebacic acid. Another monomer based on castor oil is 11-aminoundecanoic acid. From castor oil to bioplastic Castor oil is a vegetable oil extracted from the castor bean (or better from the castor seed as the castor plant, Ricinus communis, is not a member of the bean family Fabaceae; it is a member of the Euphorbiaceae). Castor oil ranges from colorless to very pale yellow liquid with mild or no odor or taste. Its boiling point is 313°C and its density is 0.961 kg/cm 3 [1]. After the oil extraction, the Castor meal (also known as Castor cake) is separated and the oil is subsequently hydrolyzed to a mixture of glycerine and ricinoleic acid in the refining process. Ricinoleic acid, a monounsaturated, 18-carbon fatty acid, is unusual compared to other fatty acids due to its hydroxyl functional group on the 12th carbon. This functional group renders ricinoleic acid unusually polar, and also increases its chemical reactivity, a property that is unique when compared with most of the others vegetable oils. It is the hydroxyl group which makes castor oil and ricinoleic acid susceptible of an easy chemical derivatization, thus a valuable chemical feedstocks [2]. In a next step (see Fig. 2) the ricinoleic acid is converted into either undecenoic acid (monomer for PA11) or sebacic acid (one of the monomers for PA6.10 and PA10.10). This sebacic acid (or decanedioic acid (the IUPAC name), or 1,8-octanedicarboxylic acid or C 10 H 18 O 4 or [HOOC(CH 2 )8COOH]) is a dicarboxylic acid that can for example be used as monomer for different types of HO O where each corner represents a methylene-group (CH 2 ) Sebacic acid polyamides [3]. In the commercially available polyamides PA 4.10, and PA 6.10, the ‘10’-component is based on this dicarboxylic acid with 10 carbon atoms. Since the other component (the diamine) in these resins usually is not made from renewable resources, these partly biobased polyamides have 63% (PA 6.10) or 70% (PA4.10) biobased content. Polyamides 5.10 (not yet commercially available), PA 10.10 and PA 10.12 can be 100% biobased as here the diamine can be derived from renewable resources as well. In the case of PA 10.10 both monomers (1,10-decamethylene diamine and sebacic acid) are derived from castor oil [8]. A third example is PA 11. Here a single monomer is being used. First the ricinoleic acid from the castor oil is converted into undecanoic acid [H 2 C=CH-(CH 2 )-COOH] via a catalytic reaction (methanolysis). This is then further converted into 11-aminoundecanoic acid in a subsequent catalytically supported reaction with ammonia [9]. This 100% biobased polyamide has been discovered and marketed since as far back as 1947 [3]. Sebacic acid is also found as ingredient in the cosmetic industry, as thickeners for coatings and lubricants, as antifreeze for lubricants, as plastizers, stabilizers, anticorrosion chemicals or other polymers such as polyols and polyesters and many other uses. O OH 48 bioplastics MAGAZINE [03/12] Vol. 7
Basics Fig 2: Principle sketch: from castor oil to sebacic acid (according to Evonik) Castor Seeds Ricinus Cumminus Waste or By-Product Main Constitute or Final Product Hulls/Shells Mechanical Pressing Castor Oil Triacylglycerol Meal/Cake Glycerin Solvent Extraction/Refining HO OH OH Ricinoleic Acid 12-Hydroxyoctade c-9-enoic acid O OH OH Heptaldehyde O H Pyrolysis Undecenoic Acid 10-undecenoic acid Alkali Fission Sebacic Acid 1,8-octanedicarboxylic acid 2-Octanol OH Fig 3: Castor plant O OH O HO OH O About the castor plant The castor oil plant, Ricinus communis, is a species of flowering plant in the spurge family, Euphorbiaceae. It belongs to a monotypic genus, Ricinus, and subtribe, Ricininae. The evolution of castor and its relation to other species are currently being studied [4]. Castor is indigenous to the southeastern Mediterranean Basin, Eastern Africa, and India, but is widespread throughout tropical regions (and widely grown elsewhere as an ornamental plant) [5]. Throughout the growth season, the castor oil responds well to temperatures between 20 – 26°C with a low humidity and grows best in loamy soils with medium texture. Nonetheless, castor plants are renowned as a low maintenance crop with the ability to be cultivated especially on marginal lands and can tolerate various weather conditions. The following lists the most recent (2006 – 2010) 4-year average of the main castor bean producing regions: 1. India: 12.6 ton/ha yield and 71.6% total harvest capacity 2. China: 8.6 ton/ha yield and 13.2% total harvest capacity 3. Brazil: 6.4 ton/ha yield and 7.2% total harvest capacity There are also several smaller players/regions (the residual 8.1%) who are increasing their production and might play a role in the near future. At the moment, the market is clearly dominated by India, where the yields in castor seeds are nearly double the ones obtained in Brazil [6]. Biochemicals from castor oil do not affect food production or cause any land use change. Castor oil is toxic and thus not part of food chain, a characteristic that is drawing more and more attention lately. The castor plants grow on arid to marginal lands with little or no agrochemicals needed [7]. Castor helps in the current Polyamide 12 crisis An explosion and fire in a chemical plant in Marl, Germany on March 31 st cut a significant amount of the world’s supply of CDT (a triple-unsaturated cyclic hydrocarbon cyclododecatriene). CDT is a petrochemically based speciality resin needed for the production cycle of Polyamide 12. This PA 12 is needed among others by the automotive industry for manufacturing fuel lines, fuel tanks and brake lines due to its high resistant to brake fluid and gasoline. Some of the partly or fully biobased polyamides based on castor oil can play a significant role in this crisis, as these resins can be used as an alternative for many of the concerned applications. References [1] Aldrich Handbook of Fine Chemicals and Laboratory Equipment, Sigma-Aldrich, 2003 (found in Wikipedia) [2] Wikipedia: http://en.wikipedia.org/wiki/Castor_oil [3] Basics of Bio-polyamides, bioplastics MAGAZINE, vol 5, issue 03/2010 [4] Euphorbiaceae (spurge) genomics. Institute for Genome Sciences. University of Maryland Medical School (found in Wikipedia) [5] Phillips, Roger; Martyn Rix (1999). Annuals and Biennials. London: Macmillan. p. 106 (found in Wikipedia) [6] FAOSTAT, 2006-2009, FAO data based on imputation methodology [7] Wang, M.S., Huang, J.C., 1994, Nylon 1010 properties and applications, J. Pol. Eng., 13 (2), pp155-174 & New Crop Resource Online Program, Purdue University, http://www.hort.purdue.edu/newcrop/default.html [8] VESTAMID ® Terra - Because we care (brochure of Evonik, Marl Germany), 2012 [9] Endrich, H.-J., Siebert-Raths, Engineering Biopolymers, Carl Hanser Verlag, 2011 [10] www.usitc.gov/publications/701_731/pub3775.pdf The author is grateful to Evonik and nova-Institute for their contribution to this article. bioplastics MAGAZINE [03/12] Vol. 7 49
