Coatings Castor oil is used as a biobased
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 a rigid polyol and in coatings. Castor oil is not a
drying oil, meaning that it has a low reactivity with air compared with oils such as
linseed oil and
tung oil. However, dehydration of castor oil yields linoleic acids, which do have drying properties.
Chemical precursor Castor oil can react with other materials to produce other chemical compounds that have numerous applications.
Transesterification followed by
steam cracking gives
undecylenic acid, a precursor to specialized polymer
nylon 11, and
heptanal, a component in fragrances. Breakdown of castor oil in strong base gives
2-octanol, both a fragrance component and a specialized solvent, and the
dicarboxylic acid sebacic acid. Hydrogenation of castor oil saturates the alkenes, giving a waxy lubricant. 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. 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.
Lubrication Vegetable oils such as castor oil are typically unattractive alternatives to
petroleum-derived
lubricants because of their poor
oxidative stability. 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 racing engines. The viscosity of castor oil at is 2,420
centipoise, but it tends to form gums in a short time, so its usefulness is limited to engines that are regularly rebuilt, such as racing engines. Lubricant company
Castrol took its name from castor oil. Castor oil has been suggested as a lubricant for
bicycle pumps because it does not degrade natural rubber seals.
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. It was the first synthetic
detergent after ordinary soap. It is used in formulating lubricants, softeners, and
dyeing assistants.
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, because of its exceptionally low
cloud point and
pour point. 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.
Early aviation and aeromodelling used castor oil as a primary lubricant, mixed with the fuel. 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 in 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-fueled, two-cycle,
glow-plug engines used for aeromodelling, since their adoption by
model airplane hobbyists in the 1940s, have used varying percentages of castor oil as lubricants. 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 requiring eventual replacement of
ball bearings 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. ==Safety==