Biopolymers - Food and Industrial Bioproducts and Bioprocessing - page 273

triacylglyceride oils, fatty acid esters, and methyl esters of triacylglyceride oils. Among these
products, fatty amines and amides are industrially significant and widely used.

11.3.1.2 Polymers from castor oil

The castor oil plant ( Ricinus communis) is a native of tropical Asia and Africa. The castor oil
extraction and refining processes have been reviewed by Ogunniyi (2006) and, more recently,
by Mutlu and Meier (2010). The fatty acids generally consist of up to 90% ricinoleic, 4%
linoleic, 3% oleic, 1% stearic, and less than 1% linolenic acids. The high content of ricinoleic
acid is the reason for the high value of castor oil and its versatile application possibilities in
the chemical industry. Moreover, the hydroxyl functionality of ricinoleic acid, which makes
castor oil a natural polyol, provides oxidative stability to the oil, and a relatively high shelf
life compared to other oils by preventing the formation of peroxides. Furthermore, the
hydroxyl group allows a variety of chemical reactions to be performed on ricinoleic acid and
its derivatives, including dehydration, halogenation, alkoxylation, esterification, and
sulfation. Castor oil is already widely used for industrial chemical products like paints,
coatings, inks, lubricants, and so on.
Castor oil is often used as a polyol and reacted with various diisocyanates in order to
produce PU products, ranging from coatings, cast elastomers, thermoplastic elastomers, rigid
foams, semi-rigid foams, sealants, adhesives to flexible foams. Moreover, Moeini (2007)
reported production of novel green polyether-ester urethane and insulating coatings based on
polyols derived from glycolyzed polyethylene terephtalate (PET), castor oil, and adipic acid,
which exhibited excellent mechanical properties and electrical insulation characteristics.
Since castor oil has a low hydroxy functionality, transesterification with glycerol can improve
the properties and yield rigid PU foams with good physicomechanical properties (Petrovi ´
et al ., 2009). Furthermore, with the addition of trimethylol propane and pentaerythritol, an
even higher thermal stability was achieved (Valero et al ., 2008 ). Karak and co-workers
(2009) reported the synthesis of castor oil-modified hyperbranched thermoplastic PU. These
materials were derived from castor oil, a macroglycol (e.g. poly-

-caprolactone, (PCL)-diol
or PEG), and MDI with or without a chain extender. Castor oil-derived PUs are also of
interest for composite materials. For instance, castor oil/graphite composites were studied as
electrode materials (Mendes et al ., 2002). Moreover, when doped with sulfonated polyaniline,
electrically conductive PUs were synthesized from castor oil (Amado et al ., 2006 ).
Castor oil has found application in the synthesis of interpenetrating polymer networks
(IPNs). These materials can be defined as a combination of two polymer networks, at least
one of which is synthesized and/or cross-linked in the immediate presence of the other. They
are called semi-IPN if just one of the polymers is a network (Athawale et al ., 2003 ). Early
reports on castor oil IPNs appeared in 1977 by Yenwo and co-workers. The report discussed
the synthesis possibilities via cross-linking of double bonds with sulfur, reaction of hydroxyl
groups with diisocyanates, and emulsion polymerizations with saponified ricinoleic acids as
emulsifier. Moreover, the IPNs from acrylic polymers, such as polymethyl methacrylate and
poly-2-ethoxyethyl methacrylate, and castor oil-based polyurethanes were reported to
contribute to the final properties of the material (Cunha et al ., 2004 ; Sanmathi et al ., 2004 ).
Incorporation of acrylic moieties into the PU networks increased toughness and thermal
properties. In contrast, IPN polyesters derived from castor oil and dibasic acids (e.g. malonic,
succinic, glutaric, adipic, suberic, and sebacic acid) were obtained as soft and opaque
elastomers (Suthar et al ., 2003 ).
Mohapatra and co-workers (1996) synthesized a castor-oil based PU via isocyanates and
a novolac resin to produce semi-IPNs. Various PUs from diphenylmethane diisocyanate,

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