Castor oil

Castor oil also called caster oil is a vegetable oil obtained by pressing the seeds of the castor oil plant (Ricinus communis L.) that is often used as a lubricant and stimulant laxative and vital industrial raw material in the chemical industry ¹⁾, ²⁾, ³⁾, ⁴⁾, ⁵⁾, ⁶⁾. Relative to other vegetable oils, castor oil has a good shelf life and it does not turn rancid unless subjected to excessive heat. Ricinoleic acid, which is produced by hydrolysis of castor oil via pancreatic lipase in the small intestine, is responsible for castor oil’s laxative action. Commonly thought that stimulant laxatives induce defecation by stimulating propulsive peristaltic activity of the intestine through local irritation of the mucosa or through a more selective action on the intramural nerve plexus of intestinal smooth muscle, thus increasing motility. More recent evidence shows that castor oil alter fluid and electrolyte absorption, producing net intestinal fluid accumulation and laxation. Castor oil produces violent evacuation of the bowels in therapeutic doses. Therefore do not taking castor oil at bedtime since the laxative effect occurs quickly. Prolonged castor oil use can cause excessive loss of fluids, electrolytes, and nutrients.

Castor oil is mainly cultivated in Africa, South America, and India. As of 2008, three countries (India, China, and Brazil) produced 93% of the world’s supply of castor oil with India being world’s largest exporter of castor oil, accounting for over 90% of castor oil exports, while the United States, European Union, and China are the major importers, accounting for 84% of imported castor oil ⁷⁾, ⁸⁾. Approximately 86% of castor seed production in India is concentrated in Gujarat, followed by Andhra Pradesh and Rajasthan ⁹⁾, ¹⁰⁾.

Castor oil is known to consist of up to 90% ricinoleic, 4% linoleic, 3% oleic, 1% stearic, and less than 1% linolenic fatty acids ¹¹⁾. Castor oil is valuable due to the high content of ricinoleic acid (up to 90%), which is used in a variety of applications in the chemical industry ¹²⁾. The hydroxyl functionality of ricinoleic acid makes the castor oil a natural polyol providing oxidative stability to the oil, and a relatively high shelf life compared to other oils by preventing peroxide formation. The presence of the hydroxyl group in ricinoleic acid and ricinoleic acid derivatives provides a functional group location for performing a variety of chemical reactions including halogenation, dehydration, alkoxylation, esterification, and sulfation ¹³⁾. As a result, this unique functionality allows the castor oil to be used in industrial applications such as paints, coatings, inks, and lubricants ¹⁴⁾.

Castor beans (Ricinus communis beans), the source of castor oil, are processed throughout the world to make castor oil. Castor oil seed contains about 30%–50% oil (m/m) ¹⁵⁾. Castor oil can be extracted from castor beans by either mechanical pressing, solvent extraction, or a combination of pressing and extraction ¹⁶⁾. After harvesting, castor beans (Ricinus communis beans) are allowed to dry so that the seed hull will split open, releasing the seed inside. The extraction process begins with the removal of the hull from the seeds. This can be accomplished mechanically with the aid of a castor bean dehuller or manually with the hands. When economically feasible, the use of a machine to aid in the dehulling process is more preferable.

Castor beans (Ricinus communis beans) contain some allergenic (2S albumin) proteins as well as ricin (a poison found naturally in castor beans) and ricine; however, processed or refined castor oil is free from ricin and can be safely used in pharmaceutical applications ¹⁷⁾, ¹⁸⁾, ¹⁹⁾, ²⁰⁾, ²¹⁾, ²²⁾. Ricin (a poison found naturally in castor beans) is found exclusively in the endosperm of castor seeds and is classified as a type 2 ribosome-inactivating protein ²³⁾, ²⁴⁾. Type 2 ribosome-inactivating proteins such as ricin from castor oil are lectins, which irreversibly inactivate ribosomes, thus stopping protein synthesis and eventually leading to cell death. This makes ricin a potent plant toxin ²⁵⁾.

Ricin is a poison found naturally in castor beans. Ricin can be used to poison people by putting it in food or water. If liquid or powdered ricin is released into the air, people could be poisoned by inhaling it. If it’s mixed with a solvent, it can be absorbed through the skin, although that’s probably the least likely way to be poisoned with ricin. Ricin can also be used to poison an individual person by injecting it. Ricin works by getting inside the cells of a person’s body and preventing the cells from making the proteins they need. Without the proteins, cells die. Eventually this is harmful to the whole body, and may cause death. If castor beans (Ricinus communis beans) are chewed and swallowed, the released ricin can cause injury. People have been poisoned with ricin after eating castor beans, but most cases of eating castor beans do not result in poisoning, because it is difficult to release the ricin from castor beans. Also, ricin is not as well absorbed through the gastrointestinal tract when compared to injection or inhalation.

Figure 1. Castor beans (Ricinus communis beans)

Table 1. Castor oil physical properties

Castor oil physical properties
Viscosity	889.3 centistokes
Density	0.959 g/mL
Thermal conductivity	4.727 W/m°C
Specific heat	0.089 kJ/kg/K
Flash point	145 °C
Pour point	2.7 °C
Melting point	−2 to −5 °C
Refractive index	1.48

[Source ²⁶⁾ ]

Castor oil uses

While castor oil is well known as a powerful laxative, the medicinal use of the oil is relatively minor (<1%). Castor oil is considered to be an important feedstock utilized by the chemical industry, particularly in producing a wide array of materials, many of which are superior to equivalent products derived from petroleum. The high percent composition of ricinoleic acid in proximity to the double bond makes castor oil poised for various physical, chemical, and even physiological activities ²⁷⁾.

In modern-day medicine, castor oil is also used as a drug delivery vehicle. An example is Kolliphor EL (Cremophor EL), which is a registered product of BASF Corp. The product is a polyexthoxylated castor oil, a mixture (CAS No. 61791-12-6) that is prepared when 35 moles of ethylene oxide is made to react with one mole of castor oil. This product is often used as an excipient or additive in drugs and is also used to form stable emulsions of nonpolar materials in various aqueous systems. It is also often used as a drug delivery vehicle for very nonpolar drugs such as the anticancer drugs paclitaxel and docetaxel ²⁸⁾, ²⁹⁾, ³⁰⁾.

Castor oil can be found in these products:

• Castor oil
• Alphamul
• Emulsoil
• Fleet Flavored Castor Oil
• Laxopol
• Unisol

Other products may also contain castor oil.

Constipation

Castor oil is a strong stimulant laxative. Castor oil has been used as a stimulant laxative to relieve occasional constipation. Most effective when administered on an empty stomach. Loose bowel movements usually occur within 2 to 3 hours (range: 2 to 6 hours) following oral administration. However, castor oil usually is avoided for simple constipation because it produces violent evacuation of the bowels. Castor oil has been used to treat constipation that occurs following prolonged bed rest or hospitalization. Castor oil has been used to treat constipation occurring secondary to idiopathic slowing of transit time, to constipating drugs, or to irritable bowel syndrome or spastic colon syndrome. Castor oil has been used to treat constipation in patients with neurologic constipation.

Castor oil has been used to treat constipation resulting from diminished colonic motor response in geriatric patients but, because this type of constipation is frequently due to psychological or physical laxative dependence, the bulk-forming laxatives such as ispaghula husk and methylcellulose, which work in the same way as dietary fiber as they increase the bulk of your stools (poops) by helping them retain fluid, encouraging your bowels to push the stools out are preferred.

Colonic evacuation

Castor oil used orally to empty the bowel prior to surgery or radiologic, sigmoidoscopic, or proctoscopic procedures, when thorough evacuation is essential.

Usually castor oil is supplemented with administration of rectal evacuants, such as saline, stimulant, or soapsuds enemas, immediately before radiologic procedures.

Castor oil uses in chemical industry

Fuel and biodiesel

Few studies have been done regarding castor fuel-related properties in pure form or as a blend with diesel fuel, primarily due to the extremely high content of ricinoleic acid. In a study by Berman et al ³¹⁾, it was found that methyl esters of castor oil can be used as a biodiesel alternative feedstock when blended with diesel fuel. However, the maximum blending level is limited to 10% due to the high levels of ricinoleic acid present in castor oil, which directly affects biodiesel’s kinematic viscosity and distillation temperature. Another study by Shojaeefard et al ³²⁾ examined the effects of castor oil biodiesel blends on diesel engine performance and emissions. They found that a 15% blend of castor oil–biodiesel was an optimized blend of biodiesel–diesel proportions. The results indicated that lower blends of biodiesel provide acceptable engine performance and even improve it.

Similar to the study by Shojaeefard et al ³³⁾, Panwar et al ³⁴⁾ prepared the castor methyl ester by transesterification using potassium hydroxide (KOH) as catalyst. They then tested this methyl ester by using it in a four-stroke, single cylinder variable compression ratio type diesel engine. It was concluded that the lower blends of biodiesel increased the break thermal efficiency and reduced the fuel consumption. Furthermore, the exhaust gas temperature increased with increasing biodiesel concentration. Results of their study proved that the use of biodiesel from castor seed oil in a compression ignition engine is a viable alternative to diesel. The transesterification reactions of castor oil with ethanol and methanol as transesterification agents were also studied in the presence of several classical catalytic systems. Results of their study show that biodiesel can be obtained by transesterification of castor oil using either ethanol or methanol as the transesterification agents ³⁵⁾.

Although these studies have shown promising results for the use of castor oil as a technically feasible biodiesel fuel, a major obstacle still exists in its use as a biodiesel in some countries such as Brazil. In Brazil, government policies promoted castor as a biodiesel feedstock in an attempt to bring social benefits to small farmers in the semiarid region of the country ³⁶⁾, ³⁷⁾. However, seven years after the Brazilian biodiesel program was launched, negligible amounts of castor oil have been used for biodiesel production. It was found that the castor oil produced in this program was not primarily used for biodiesel but sold for higher prices to the chemical industry ³⁸⁾. Another major constraint in the use of castor oil as a feedstock for biodiesel has been the high price paid for the oil as industrial oil rather than its physical and chemical properties. Castor oil is in high demand by the chemical industry for the manufacture of very high value products. For this reason, it is not economical to use castor oil as a replacement for diesel ³⁹⁾. Lastly, although castor oil can be used directly to replace normal diesel fuel, the high viscosity of this oil limits its application ⁴⁰⁾.

Polymer materials

Castor oil and its derivatives can be used in the synthesis of renewable monomers and polymers ⁴¹⁾. In one study, castor oil was polymerized and cross-linked with sulfur or diisocyanates to form the vulcanized and urethane derivatives, respectively ⁴²⁾. In another study, full-interpenetrating polymer networks (IPNs) were prepared from epoxy and castor oil-based polyurethane (PU), by the sequential mode of synthesis ⁴³⁾. Similar to the aforementioned study, a series of two-component interpenetrating polymer network of modified castor oil-based polyurethane and polystyrene were prepared by the sequential method ⁴⁴⁾. Interpenetrating polymer network can be elaborated as a special class of polymers in which there is a combination of two polymers in which one is synthesized or polymerized in the presence of another ⁴⁵⁾, ⁴⁶⁾. Therefore, interpenetrating polymer network formulation can be considered a useful method to develop a product with excellent physicomechanical properties than the normal polyblends. Interpenetrating polymer network (IPN) is also known as polymer alloys and is considered to be one of the fastest growing research areas in the field of polymer blends in the last two decades ⁴⁷⁾.

Castor oil polymer (COP) has also been shown to have a sealing ability as a root-end filling material in endodontics. A root-end filling material simply refers to root-end preparations filled with experimental materials. The main objective of this type of material is to provide an apical seal preventing the movements of bacteria and the diffusion of bacterial products from the root canal system into the periapical tissues ⁴⁸⁾. In a study conducted by de Martins et al ⁴⁹⁾, the sealing ability of castor oil polymer (COP), mineral trioxide aggregate (MTA), and glass ionomer cement (GIC) as root-end filling materials were evaluated. Mineral trioxide aggregate (MTA) is primarily composed of tricalcic silicate, tricalcic alluminate, and bismuth oxide and is a particular endodontic cement ⁵⁰⁾. Glass ionomer cements (GICs), on the other hand, are mainstream restorative materials that are bioactive and have a wide range of uses such as lining, bonding, sealing, luting, or restoring a tooth ⁵¹⁾. Results of their study show that the castor oil polymer had a greater sealing ability when used as a root-end filling material than mineral trioxide aggregate (MTA), and glass ionomer cement (GIC).

Biodegradable polyesters are one of the most common applications using castor oil ⁵²⁾. Polyesters are the first synthetic condensation polymers prepared by Carothers during the 1930s ⁵³⁾, ⁵⁴⁾. They are known to be biodegradable and environmental friendly, with a wide array of applications in the biomedical field, as well in the preparation of elastomers and packaging materials ⁵⁵⁾, ⁵⁶⁾. Fatty acid scaffolds are desirable biodegradable polymers, though they are restricted by their monofunctional property. That is, most fatty acids have a single carboxylic acid group. ricinoleic acid, however, is known to be one of the few naturally available bifunctional fatty acids with an additional 12-hydroxy group along with the terminal carboxylic acid. The presence of this hydroxyl group provides additional functionality for the preparation of polyesters or polyester-anhydrides. The dangling chains of the ricinoleic acid impart hydrophobicity to the resulting polyesters, thereby influencing the mechanical and physical property of the polymers. These chains act as plasticizers by reducing the glass transition temperatures of the polyesters ⁵⁷⁾, ⁵⁸⁾. Castor oil can be combined with other monomers to produce an array of copolymers. Fine-tuning these copolymers can provide materials with different properties that find use in products ranging from solid implants to in situ injectable hydrophobic gel ⁵⁹⁾.

Soaps, waxes, and greases

Castor oil has been used to produce soaps in some studies ⁶⁰⁾, ⁶¹⁾, ⁶²⁾. Some studies also utilize castor oil in waxes ⁶³⁾, ⁶⁴⁾, ⁶⁵⁾, ⁶⁶⁾. One study by Dwivedi and Sapre ⁶⁷⁾ utilized castor oil in total vegetable oil greases. Total vegetable oil greases are those in which both the lubricant and gellant are formed from vegetable oil. Their study utilized a simultaneous reaction scheme to form sodium and lithium greases using castor oil.

Lubricants, hydraulic, and brake fluids

Castor oil has also been used for developing low pour point lubricant base stocks through the synthesis of acyloxy castor polyol esters ⁶⁸⁾. The low pour point property helps to provide full lubrication when the equipment is started and is easier to handle in cold weather ⁶⁹⁾. An interesting study by Singh ⁷⁰⁾ showed the excellent potential of castor oil-based lubricant as a smoke pollution reducer. In his research, a biodegradable two-stroke (2T) oil, a popular variety of lubricating oil used on two-stroke engines in scooters and motorcycles ⁷¹⁾ , was developed from castor oil, which consisted of tolyl monoesters and performance additives, but no miscibility solvent. Their performance evaluations showed that it reduced smoke by 50%–70% at a 1% oil–fuel ratio, and it was on par with standard product specification ⁷²⁾. In addition to the possible use as a car engine lubricant, a modified version of castor oil lubricant comprising 100 parts of castor oil and 20–110 parts of a chemically and thermally stable, low viscosity blending fluid, soluble in castor oil showed its potential as a lubricant for refrigerator systems ⁷³⁾. Although castor oil has been used as a DOT 2 rating brake fluid, it is considered an outdated type of brake fluid that should not be used in any modern vehicles ⁷⁴⁾, ⁷⁵⁾.

Fertilizers

Production of castor oil generates two main byproducts: husks and meal. For each ton of castor oil, 1.31 tons of husks and 1.1 tons of meal are generated. A study by Lima et al ⁷⁶⁾ showed that blends of castor meal and castor husks used as fertilizer promoted substantial plant growth up to the dose of 4.5% (in volume) of meal. However, doses exceeding 4.5% caused reduction in plant growth and even plant death. Their study showed that castor meal may be used as a good organic fertilizer due to its high nitrogen and phosphorus content, but blending with castor husks is not necessary.

Coatings

Coatings and paints are also another application of castor oil. Castor oil can be effectively dehydrated by nonconjugated oil–maleic anhydride adducts to give useful paint or furniture oil applications ⁷⁷⁾. Trevino and Trumbo ⁷⁸⁾ studied the utilization of castor oil as a coating application by converting the hydroxyl functionalities of castor oil to beta-ketoesters using t-butyl acetoacetate. The reaction is known to be relatively rapid and proceeded to high yield under mild conditions. Results showed that the 60° glosses of the films and film flexibilities were good. In a separate study by Thakur and Karak ⁷⁹⁾, advanced surface coating materials were synthesized from castor oil-based hyperbranched polyurethanes (HBPUs), a highly branched macromolecule. The hyperbranched polyurethanes (HBPUs) exhibited excellent performance as surface coating materials with the monoglyceride-based HBPU, exhibiting higher tensile strength than direct oil-based coatings. Both the HBPUs have acceptable dielectric properties with greater than 250°C thermal stability for both the polymers. Ceramer coatings are also another coating application of castor oil. de Luca et al ⁸⁰⁾ synthesized ceramer coatings from castor oil or epoxidized castor oil and tetraethoxysilane. Most recently, high-performance hybrid coatings were synthesized by Allauddin et al ⁸¹⁾ using a methodology that included introducing hydrolyzable –Si-OCH3 groups onto castor oil that have been used for the development of polyurethane/urea–silica hybrid coatings.

Castor oil side effects

Normally, castor oil should cause few problems. Castor oil common side effects include:

• Abdominal discomfort, nausea, cramps, griping, and/or faintness.
• Even at therapeutic doses, excessive irritation of the colon and violent violent evacuation of the bowels.
• Diarrhea, gastrointestinal irritation, and fluid and electrolyte depletion.
• May rarely cause pelvic congestion.

Chronic castor oil use or castor oil overdose may produce persistent diarrhea, low blood potassium (hypokalemia), loss of essential nutritional factors, and dehydration. Electrolyte disturbances including low blood potassium (hypokalemia), low blood calcium (hypocalcemia), metabolic acidosis or alkalosis, abdominal pain, diarrhea, malabsorption, weight loss, and protein-losing enteropathy may occur.

Symptoms of a castor oil overdose include:

• Abdominal cramps
• Chest pain
• Diarrhea
• Dizziness
• Hallucinations (rare)
• Fainting
• Nausea
• Shortness of breath
• Skin rash
• Throat tightness

Electrolyte disturbances may produce vomiting and muscle weakness; rarely, osteomalacia, secondary aldosteronism, and tetany may occur.

Pathologic changes including structural damage to the myenteric plexus, severe and permanent interference with colonic motility, and hypertrophy of the muscularis mucosae may occur with chronic use.

Protein-losing enteropathy and steatorrhea can occur.

“Cathartic colon” with atony and dilation of the colon, especially of the right side, has occurred with habitual use (often for several years) and often resembles ulcerative colitis.

In rural India, castor oil has been traditionally given to infants during the first 2 to 3 days of life to clear the intestine of a newborn’s first poop also known as meconium. This practice can result in paralysis of the digestive tract (paralytic ileus) and aspiration pneumonia (pneumonia that occurs when food or liquid is breathed into the airways or lungs, instead of being swallowed)⁸²⁾. Severe hypoalbuminemia (low level of albumin in the blood) was also reported in a 1.5-month-old infant whose grandmother gave him castor oil daily from the fifth day of life, resulting in diarrhea and malnutrition ⁸³⁾.

Ricinus communis (castor oil plant) contain the toxin ricin. Purified ricin derived from the castor bean is highly toxic and lethal in small doses.

Castor oil contraindications

Castor oil is contraindicated in acute abdominal pain, nausea, vomiting, or other symptoms of appendicitis or undiagnosed abdominal pain or rectal bleeding.

Castor oil is contraindicated in intestinal obstruction.

Castor oil is contraindicated in pregnancy (Category X) or menstruation. Category X drugs have such a high risk of causing permanent damage to the fetus that they should not be used in pregnancy or when there is a possibility of pregnancy.

Is castor oil safe?

Castor oil is not considered very toxic, but allergic reactions are possible and large amounts of castor oil can be poisonous.

Castor beans (Ricinus communis beans) are processed throughout the world to make castor oil. Pressing of the Ricinus communis beans (castor beans) produces castor oil and purification of the oil eliminates ricin (a poison found naturally in castor beans) and ricine. Ricin is a poison found naturally in castor beans ⁸⁴⁾, ⁸⁵⁾, ⁸⁶⁾, ⁸⁷⁾, ⁸⁸⁾, ⁸⁹⁾. Ricin works by getting inside the cells of a person’s body and preventing the cells from making the proteins they need. Without the proteins, cells die. Eventually this is harmful to the whole body, and may cause death. If castor beans (Ricinus communis beans) are chewed and swallowed, the released ricin can cause injury. People have been poisoned with ricin after eating castor beans, but most cases of eating castor beans do not result in poisoning, because it is difficult to release the ricin from castor beans. Also, ricin is not as well absorbed through the gastrointestinal tract when compared to injection or inhalation.

Ricin can be made from the waste material or the waste “mash” left over from processing castor beans. Ricin can be in the form of a dry powder, a mist,  crystals or a pellet, or it can be dissolved in water or weak acid. It’s very unlikely that anyone would ever be poisoned with ricin by accident. It would only happen if someone used ricin on purpose. Ricin has been used experimentally in medicine to kill cancer cells. Ricin is a stable substance under normal conditions, but can be inactivated by heat above 80 degrees centigrade (176 degrees Fahrenheit).

Ricin poisoning can cause death, but it isn’t always fatal. Signs and symptoms of ricin exposure depend on the route of exposure and the dose received, though many organs may be affected in severe cases ⁹⁰⁾, ⁹¹⁾:

• Initial symptoms of ricin poisoning by inhalation may occur as early as 4 to 8 hours and as late as 24 hours after exposure. Following ingestion of ricin, initial symptoms typically occur in less than 10 hours.
• Inhalation: A person who inhales ricin will develop a cough within 3 hours. Inhaling significant amounts of ricin, the likely symptoms would be respiratory distress (difficulty breathing), fever, cough, nausea, and tightness in the chest. Nausea, diarrhea, and aches and pains will follow within 18 to 24 hours. If the dose is big enough, death will occur within 36 to 72 hours – from damage to the heart and blood vessels, and fluid in the lungs (pulmonary edema). Fluid building up in the lungs (pulmonary edema) would make breathing even more difficult, and the skin might turn blue. Excess fluid in the lungs can be diagnosed by x-ray or by listening to the chest with a stethoscope. Finally, low blood pressure and respiratory failure may occur, leading to death. In cases of known exposure to ricin, people having respiratory symptoms should seek medical care.
• Injection. Injecting ricin will destroy muscles around the injection site right away. Death follows quickly, from failure of major organs in the body.
• Skin and eye exposure: Ricin is unlikely to be absorbed through normal skin. Absorbing ricin through the skin is the least likely way anyone would be exposed to the poison – and the least likely to cause death. Contact with ricin powders or products may cause redness and pain of the skin and the eyes. However, if you touch ricin that is on your skin and then eat food with your hands or put your hands in your mouth, you may ingest some.
• Ingestion: Ricin in food or water can cause very severe “food poisoning” symptoms – including vomiting and diarrhea that may become bloody. It also affects the liver and kidneys. Severe dehydration may be the result, followed by low blood pressure. Other signs or symptoms may include seizures, and blood in the urine. Within several days, the person’s liver, spleen, and kidneys might stop working, and the person could die. If the dose is big enough, it can kill within three days. One milligram of ricin, in food or water, can kill an adult.
• Death from ricin poisoning could take place within 36 to 72 hours of exposure, depending on the route of exposure (whether poisoning was by inhalation, ingestion, or skin or eye exposure or injection) and the dose received.

Right now, there is no antidote for ricin, but the symptoms of ricin poisoning can be treated. Treatment will depend on how the patient was exposed to ricin, but may include helping victims breathe, giving them intravenous fluids (fluids given through a needle inserted into a vein), giving them medications to treat conditions such as seizure and low blood pressure, flushing their stomachs with activated charcoal (if the ricin has been very recently ingested), or washing out their eyes with water if their eyes are irritated ⁹²⁾, ⁹³⁾. People who survive ricin poisoning more than five days have a good chance of recovering ⁹⁴⁾.