Castor oil

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Castor beans.

Castor oil (castor is Latin for beaver - before it was discovered in plants, castor oil was extracted from beavers groin [1]) is a vegetable oil obtained from the castor bean (technically castor seed as the castor plant, Ricinus communis (Euphorbiaceae), is not a member of the bean family). Castor oil is a colorless to very pale yellow liquid with mild or no odor or taste. Its boiling point is 313 °C (595 °F) and its density is 961 kg/m3.[2] It is a triglyceride in which approximately 90 percent of fatty acid chains are ricinoleic acid. Oleic and linoleic acids are the other significant components.[3]

Contents

Background

Structure of the major component of castor oil.

Ricinoleic acid, a monounsaturated, 18-carbon fatty 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 unusually polar, and also allows chemical derivatization that is not practical with most other seed oils. It is the hydroxyl group which makes castor oil and ricinoleic acid valuable as chemical feedstocks. Compared to other seed oils which lack the hydroxyl group, castor oil commands a higher price. As an example, in July 2007, Indian castor oil sold for about US$0.90 per kilogram (US$0.41 per pound)[4] while U.S. soybean, sunflower and canola oil sold for about US$0.30 per kilogram (US$0.14 per pound).[5]

Industry uses yearly 600-800 million pounds of castor oil and 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.[6]

The castor seed contains ricin, a toxic protein. Heating during the oil extraction process denatures and inactivates the protein. However, harvesting castor beans may be not without risk.[7] 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.[8] 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.[9][10] Alternatively, some researchers are trying to genetically modify the castor plant to prevent the synthesis of ricin.[11]

Castor oil fatty acids

Average composition of castor seed oil / fatty acid chains
Acid nameAverage Percentage Range
Ricinoleic acid95to85%
Oleic acid6to2%
Linoleic acid5to1%
Linolenic acid1to0.5%
Stearic acid1to0.5%
Palmitic acid1to0.5%
Dihydroxystearic acid0.5to0.3%
Others0.5to0.2%

Uses

Castor oil in polyurethane

Castor oil can be used as bio-based polyol in the polyurethane industry. The average functionality of castor oil is 2.7, so it is widely used as rigid polyol of polyurethane industry.

Castor oil in food

In the food industry, castor oil (food grade) is used in food additives,[12] flavorings, candy (e.g., Polyglycerol polyricinoleate or PGPR in chocolate),[13] as a mold inhibitor, and in packaging. Polyoxyethylated castor oil (e.g., Kolliphor EL)[14] is also used in the food industries.[15]

As food grain preservative

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. Also, by applying castor oil, the food becomes easy to digest.[citation needed]

Medicinal use of castor oil

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.[16] Castor oil is a stimulant and lubricating laxative[citation needed]. It is not a preferred treatment, because it can produce painful cramps, fecal incontinence and explosive diarrhea. Its action can go on for hours, sometimes unpredictably and powerfully causing an involuntary bowel movement at inconvenient locations and during sleep.[17]

Undecylenic acid, a castor oil derivative, is also FDA-approved for over-the-counter use on skin disorders or skin problems.[18] Castor oil penetrates deep into the skin due to its molecular mass, which is low enough to penetrate into the stratum corneum. Castor isostearate succinate is a polymeric mixture of esters with isostearic acid and succinic acid used for skin conditioning, such as in shampoo, lipstick and lip balm.[19]

Ricinoleic acid is the main component of castor oil, and it exerts anti-inflammatory effects.[20] It is believed that the antibacterial properties of the castor oil are mainly due to its high ricinoleic acid content.[21]

One study has found castor oil decreased pain more than ultrasound gel or Vaseline during extracorporeal shockwave application.[22]

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:

Traditional or holistic medicines

The use of cold pressed castor oil in folk medicine predates government medical regulations. It is tasteless and odorless when pure. Its uses include skin disorders, burns, sunburns, cuts, and abrasions. It has been used to draw out styes in the eye by pouring a small amount into the eye and allowing it to circulate around the inside of the eyelid. Note that most bottles of castor oil indicate it is to be kept away from the eyes. The oil is also used as a rub or pack for various ailments, including abdominal complaints, headaches, muscle pains, inflammatory conditions, skin eruptions, lesions, and sinusitis. A castor oil pack is made by soaking a piece of flannel in castor oil, then putting it on the area of complaint and placing a heat source, such as a hot water bottle, on top of it. This remedy was often suggested by the American psychic Edgar Cayce, given in many healing readings in the early mid-1900s. Castor oil has also been noted for its acne-healing abilities.[citation needed] (See Oil cleansing method.)

The use of castor oil to induce labor is controversial. One study showed that women who receive castor oil have an increased likelihood of initiation of labor within 24 hours compared to women who receive no treatment( Following administration of castor oil, 30 of 52 women (57.7%) began active labor compared to 2 of 48 (4.2%) receiving no treatment).[32] However, another study showed that castor oil had no effect on the time to birth in women whose pregnancy exceeds 40 weeks.[33]

Castor oil, when ingested, triggers cramping in the bowel, making it an effective laxative. Thus, it is intended that such cramping extend to the uterus. In an overdue pregnancy in which the mother's cervix is already effacing and partially dilated, this cramping can lead to labor contractions.[citation needed] The irregular, painful contractions of castor oil-induced labor can be stressful on the mother and fetus.[citation needed] It also leaves the laboring woman quite dehydrated as a result of the vomiting and diarrhea which result when the recommended dose of castor oil for labor induction is taken—2 oz, or about 4 tbsp.[citation needed] This leaves her without access to the energy she could otherwise derive from food or drink throughout her labor process. Using castor oil for induction is not recommended without consulting a medical practitioner and is not recommended in a complex pregnancy.[citation needed]

Ricinus communis var minor, administered orally once to each of 12 women volunteers at a dose of 2.5-2.7 g per 8 months, protected against pregnancy over a period of 7–8 months of study.[34]

In Ayurvedic medicine it is used to enhance memory.[35] In Ayurvedic medicine it is used to treat "Pitta Dosha" by using "Virechana therapy". Castor oil has also been claimed to promote eyelash growth; there is, however, no supporting scientific data.[36]

Orthopedics

The use of the castor oil-based polyurethane has been expanded into medicine, specifically in orthopedics. In the search for a new material that could be used as a bone substitute, the Analytic Chemistry and Polymer Technology Group of the University of São Paulo's São Carlos School of Engineering developed a polyurethane derived from castor oil in 1984. Experimental studies have confirmed the polyurethane potential for some orthopedic procedures both in human medicine[citation needed] and in veterinary medicine.[37]

Natural body coolant

Castor oil on application in the lower abdomen, legs and hands, and in palms have been proven to reduce body heat. The urinary problems arising because of body heat and summer will be relieved on application and in few minutes.

Industrial castor oil

Castor oil has numerous applications in transportation, cosmetics and pharmaceutical, and manufacturing industries, for example: adhesives,[38] brake fluids,[39] caulks, dyes,[38] electrical liquid dielectrics, humectants,[38] Nylon 11 plastics,[38] hydraulic fluids, inks,[38] lacquers, leather treatments,[38] lubricating greases, machining oils, paints,[38] pigments, polyurethane adhesives,[40] refrigeration lubricants, rubbers,[38] sealants, textiles,[38] washing powders, and waxes.

Since it has a relatively high dielectric constant (4.7), highly refined and dried castor oil is sometimes used as a dielectric fluid within high performance high voltage capacitors.

Lubricants

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.[41] 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.[42] 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[43]) in case of an accidental release. The lubricants company Castrol took its name from castor oil.

Castor oil is the preferred lubricant for bicycle pumps, most likely because it does not dissolve natural rubber seals.[44]

Uses in early aviation and aeromodelling

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 builds up too much within the engine's bearing races. One British manufacturer of sleeve valved four-cycle model engines has, however, 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 derivatives

Castor oil is the raw material for the production of a number of chemicals, notably sebacic acid, undecylenic acid, nylon-11. A review listing numerous chemicals derived from castor oil is available.[45][46] 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.[47]

Other derivatives are produced by first transesterification of the castor oil to methyl ricinoleate, followed by steam cracking to methyl undecylenate and n-heptaldehyde.[48]

Turkey red oil

Turkey red oil, also called sulphonated (or sulfated) castor oil, is made by adding sulfuric acid to vegetable oils, most notably castor oil.[49] It was the first synthetic detergent after ordinary soap. It is used in formulating lubricants, softeners, and dyeing assistants.[50]

Biodiesel

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.[51]

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.[52]

Use as a means of intimidation in Fascist Italy and Spain

In Fascist Italy under the regime of Benito Mussolini, castor oil was one of the tools of the Blackshirts.[53][54][55] 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.[56]

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. 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.[57]

Linguistic connotations

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, the force-feeding with castor oil still lives on in animated cartoons such as Tom and Jerry.

See also

References

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External links