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Dehydrated Castor Oil (DCO)

Dehydration of castor oil is carried out at about 250 degree Celsius in the presence of catalysts (e.g., concentrated sulphuric acid, activated earth) and under an inert atmosphere or vacuum. Under this condition of dehydration, the hydroxyl group and adjacent hydrogen atom from the C-11 or C-13 position of the ricinoleic acid portion of the molecule is removed as water. This yields a mixture of two acids, each containing two double bonds but in one case, they are conjugated.

The presence of an acid containing conjugated double bonds results in an oil resembling tung oil in some of its properties. Thus, castor oil, which is non-drying, can be treated and converted into a semi-drying or drying oil known as dehydrated castor oil.

By far the most important coatings use of castor oil is in the form of dehydrated castor. In commercial manufacture of dehydrated castor oil, the aim is to produce the most valuable material for use as a drying oil. Dehydrated castor oil is now recognized as an individual drying oil with its own characteristic properties and advantages. The drying oils owe their value as raw materials for decorative and protective coatings to their ability to polymerize or “dry” after they have been applied to a surface to form tough, adherent, impervious, and abrasion resistance films. The advantages claimed in surface coating applications include excellent odor and heat bleachability, good drying properties, more uniform polymer structure, and lack of after-yellowing.

DCO has advantages over tung oil because it is non-yellowing.

DCO can be converted to dehydrated castor fatty acid by hydrolysis and distillation. This (dehydrated castor fatty acid) is used in the manufacture of alkyd resins, coatings, appliance finishes, primers and inks. Alkyd resins in turn are used for paints, enamels, lacquers and varnishes with high gloss, good adhesion and wetting qualities.

The vulcanization of DCO with sulphur has been reported: factice, the resulting product, has been found to be a rubber additive with antiozonant and good flow properties.

If DCO is epoxidized, the product can be evaluated in poly (vinyl) compounds as a plasticizer/stabilizer, giving rise to the possibility that epoxidized castor oil may be capable of replacing epoxidized soybean oil.


·         DCO can be used to improve the quality of house paints, enamels, caulks, sealants and inks. It is used as primary binder for house paints, enamels, caulk sealant, and making varnishes.

·         This oil also works well in clear varnishes and hard finish coatings.

Physical, Chemical Properties and Specifications

CAS Number



Viscous liquid

Colour Gardner

6 Max

Acid Value

5 Max

Iodine Value

123 Min

Hydroxyl Value

25 Max

Saponification Value

185 – 194

Viscocity at 30 ºC

1.6 to 2.5 (poise 61 sec B4 cup)

Viscocity Gardner

G – J