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Castor oil is a vegetable oil obtained by pressing the seeds of the castor oil plant (Ricinus communis). The common name "castor oil", from which the plant gets its name, probably comes from its use as a replacement for castoreum, a perfume base made from the dried perineal glands of the beaver (castor in Latin).
Castor oil is a colorless to very pale yellow liquid with a distinct taste and odor once first ingested. Its boiling point is 313 °C (595 °F) and its density is 961 kg/m3. It is a triglyceride in which approximately 90 percent of fatty acid chains are ricinoleate. Oleate and linoleates are the other significant components.
Castor oil and its derivatives are used in the manufacturing of soaps, lubricants, hydraulic and brake fluids, paints, dyes, coatings, inks, cold resistant plastics, waxes and polishes, nylon, pharmaceuticals and perfumes.
Castor oil is famous as a source of ricinoleic acid, a monounsaturated, 18-carbon fatty acid. Among fatty acids, ricinoleic acid is unusual in that it has a hydroxyl functional group on the 12th carbon. This functional group causes ricinoleic acid (and castor oil) to be more polar than most fats. The chemical reactivity of the alcohol group also allows chemical derivatization that is not possible with most other seed oils. Because of its ricinoleic acid content, castor oil is a valuable chemical in feedstocks, commanding a higher price than other seed oils. As an example, in July 2007, Indian castor oil sold for about US$0.90 per kilogram (US$0.41 per pound) whereas U.S. soybean, sunflower and canola oilseeds sold for about US$0.30 per kilogram (US$0.14 per pound).
|Average composition of castor seed oil / fatty acid chains|
|Acid name||Average Percentage Range|
|Ricinoleic acid||85 – 95%|
|Oleic acid||2 – 6%|
|Linoleic acid||1 – 5%|
|α-Linolenic acid||0.5 – 1%|
|Stearic acid||0.5 – 1%|
|Palmitic acid||0.5 – 1%|
|Dihydroxystearic acid||0.3 – 0.5%|
|Others||0.2 – 0.5%|
The castor seed contains ricin, a toxic protein. Heating during the oil extraction process denatures and inactivates the protein. However, harvesting castor beans may not be without risk. Allergenic compounds found on the plant surface can cause permanent nerve damage, making the harvest of castor beans a human health risk. India, Brazil, and China are the major crop producers, and the workers suffer harmful side effects from working with these plants. These health issues, in addition to concerns about the toxic byproduct (ricin) from castor oil production, have encouraged the quest for alternative sources for hydroxy fatty acids. Alternatively, some researchers are trying to genetically modify the castor plant to prevent the synthesis of ricin.
Industry uses 270,000–360,000 tonnes (600–800 million pounds) of castor oil, annually. Its derivatives have applications in the manufacturing of soaps, lubricants, hydraulic and brake fluids, paints, dyes, coatings, inks, cold resistant plastics, waxes and polishes, nylon, pharmaceuticals and perfumes.
In the food industry, castor oil (food grade) is used in food additives, flavorings, candy (e.g., polyglycerol polyricinoleate or PGPR in chocolate), as a mold inhibitor, and in packaging. Polyoxyethylated castor oil (e.g., Kolliphor EL) is also used in the food industries.
In India, Pakistan, Nepal and Bangladesh, food grains are preserved by applying castor oil. It stops rice, wheat, and pulses from rotting. For example the legume toor dal is commonly available coated in oil for extended storage.
The United States Food and Drug Administration (FDA) has categorized castor oil as "generally recognized as safe and effective" (GRASE) for over-the-counter use as a laxative with its major site of action the small intestine where it is digested into ricinoleic acid. Despite castor oil being widely used to start labor in pregnant women, to date there is not enough research to show whether it is effective to ripen the cervix or induce labor.  Therapeutically, modern drugs are rarely given in a pure chemical state, so most active ingredients are combined with excipients or additives. Castor oil, or a castor oil derivative such as Kolliphor EL (polyethoxylated castor oil, a nonionic surfactant), is added to many modern drugs, including:
Castor oil is used as bio-based polyol in the polyurethane industry. The average functionality (number of hydroxyl groups per triglyceride molecule) of castor oil is 2.7, so it is widely used as rigid polyol and coating.
Castor oil has numerous applications in transportation, cosmetics and pharmaceutical, and manufacturing industries, for example: adhesives, brake fluids, caulks, dyes, electrical liquid dielectrics, humectants, Nylon 11 plastics, hydraulic fluids, inks, lacquers, leather treatments, lubricating greases, machining oils, paints, pigments, polyurethane adhesives, refrigeration lubricants, rubbers, sealants, textiles, washing powders, and waxes.
Vegetable oils, due to their good lubricity and biodegradability are attractive alternatives to petroleum-derived lubricants, but oxidative stability and low temperature performance limit their widespread use. Castor oil has better low temperature viscosity properties and high temperature lubrication than most vegetable oils, making it useful as a lubricant in jet, diesel, and race car engines. The viscosity of castor oil at 10 °C is 2,420 centipoise. However, castor oil tends to form gums in a short time, and its use is therefore restricted to engines that are regularly rebuilt, such as race engines. Biodegradability results in decreased persistence in the environment (relative to petroleum-based lubricants) in case of an accidental release. The lubricants company Castrol took its name from castor oil.
Castor oil was the preferred lubricant for rotary engines, such as the Gnome engine after that engine's widespread adoption for aviation in Europe in 1909. It was used almost universally by the rotary engined Allied aircraft in World War I. Germany had to make do with inferior ersatz oil for its rotary engines, which resulted in poor reliability.
The methanol-fuelled two-cycle glow plug engines used for aeromodelling, since their adoption by model airplane hobbyists in 1948, have used varying percentages of castor oil as a dependable lubricant. It is highly resistant to degradation when the engine has its fuel-air mixture leaned for maximum engine speed. Gummy residues can still be a problem for aeromodelling powerplants lubricated with castor oil, however, usually resulting in eventual ball bearing replacement when the residue accumulates within the engine's bearing races. One British manufacturer of sleeve valved four-cycle model engines has stated the "varnish" created by using castor oil in small percentages can improve the pneumatic seal of the sleeve valve, improving such an engine's performance over time.
Castor oil is the raw material for the production of a number of chemicals, notably sebacic acid, undecylenic acid, and nylon-11. A review listing numerous chemicals derived from castor oil is available. The production of lithium grease consumes a significant amount of castor oil. Hydrogenation and saponification of castor oil yields 12-hydroxystearic acid which is then reacted with lithium hydroxide or lithium carbonate to give high performance lubricant grease.
Turkey red oil, also called sulphonated (or sulfated) castor oil, is made by adding sulfuric acid to vegetable oils, most notably castor oil. It was the first synthetic detergent after ordinary soap. It is used in formulating lubricants, softeners, and dyeing assistants.
Castor oil, like currently less expensive vegetable oils, can be used as feedstock in the production of biodiesel. The resulting fuel is superior for cold winters, due to its exceptionally low cloud and pour points.
Initiatives to grow more castor for energy production, in preference to other oil crops, are motivated by social considerations. Tropical subsistence farmers would gain a cash crop.
In Fascist Italy under the regime of Benito Mussolini, castor oil was one of the tools of the Blackshirts. Political dissidents were force-fed large quantities of castor oil by Fascist squads. This technique was said to have been originated by Gabriele D'Annunzio. Victims of this treatment did sometimes die, as the dehydrating effects of the oil-induced diarrhea often complicated the recovery from the nightstick beating they also received along with the castor oil; however, even those victims who survived had to bear the humiliation of the laxative effects resulting from excessive consumption of the oil.
It is said Mussolini's power was backed by "the bludgeon and castor oil". In lesser quantities, castor oil was also used as an instrument of intimidation, for example, to discourage civilians or soldiers who would call in sick either in the factory or in the military. Since its healing properties were widely exaggerated, abuse could be easily masked under pretense of a doctor's prescription. [clarification needed] It took decades after Mussolini's death before the myth of castor oil as a panacea for a wide range of diseases and medical conditions was totally demystified, as it was also widely administered to pregnant women, elderly or mentally-ill patients in hospitals in the false belief it had no negative side effects.
It was also often used as both a punishment and torture by the Spanish Nationalists, led by Francisco Franco, as they purged Spain of those who supported the democratic, left-wing Republic during the Spanish Civil War.
Today, the Italian terms manganello and olio di ricino, even used separately, still carry strong political connotations (especially the latter). These words are still used to satirize patronizing politicians, or the authors of disliked legislation. They should be used with caution in common conversation. The terms Usare l'olio di ricino, ("to use castor oil") and usare il manganello ("to use the bludgeon") mean "to coerce or abuse", and can be misunderstood in the absence of proper context.
As a means of punishment or torture, force-feeding castor oil still lives on in animated cartoons such as Tom and Jerry.