Modified Oils

Oils are fatty acids of chains (C12 – C22) esterified with Glycerin, that, depending on the type of acid (according to the number of double bonds), will be more or less drying and reactive.

The drying oils have a large proportion of unsaturated fatty acids which, when polymerized, give a very resistant film, more adherent and shiny. The polymerization and drying process is carried out by a physical process of oxidation or thermal polymerization depending on the need of the application, to increase its viscosity, specific weight and reactivity. All drying and semi-drying oils are thermally polymerizable.

The way to determine if an oil is secant or not is by the index of Iodine (I2 / 100g): the higher the index of Iodine, the more secant it is, establishing the following scale:

  • Drying oil: from 140 I2 / 100g. Types of drying oils: Wood oil (Tung), Dehydrated Castor Oil, Linseed oil and standoils of both, Castor and Linseed oil.
  • Semi-drying oil: between 110 – 140 I2 / 100g. Types of semi-drying oils: Refined Soybean Oil.
  • Non-drying oil: lower than 110 I2 / 100g. Types of non-drying oils: Orujo oil, first pressure Castor oil and Rapeseed oil.

The composition of the oils, is a blend of fatty acids (usually the same and in different proportions), which differ from each other, depending on the amount of carbon (length of the chain) and the number of double bonds.

Fatty acid Carbon number Number of double bonds
Palmitic acid 16 0
Stearic Acid 18 0
Oleic Acid 18 1
Linoleic Acid 18 2
Linolenic Acid 18 3

As we can see, the fatty acids with double bonds (measurable from the index of Iodine), will determine the siccativity of the oil: the greater the quantity, the greater the secant power.

Given the characteristics of the starting oils, we can increase the viscosity to increase the drying rate and reactivity of the same, through the following processes:

  • Thermal polymerization: It is a physical process that maintains the starting conditions of the oil that increases the viscosity, reactivity and specific weight, decreasing the iodine index, increasing its reactivity and reducing the drawback of the yellowing of the oils contained in its composition linolenic acid. These oils are called: Polymerized / Standoils.
  • Thermal Oxipolymerization: It is a physical / chemical process that increases the viscosity, the specific weight, the surface activity, the solubility and the incorporation of oxygen bridges that saturate the double bonds. These oils are called: Oxidized / Blown.
  • Dehydrated Castor Oil: Artificial drying oil obtained by dehydroxylation of castor oil, which is characterized by a high level of iodine due to its conjugation forming a new double bond. As it does not contain linoleic acid in its composition, it avoids the possibility of yellowing due to the action of light or heat.


The oils used for industrial coatings can be classified into four sections, depending on the viscosity (drying speed / reactivity) and surface activity

  • Refined oils.
  • Polymerized oils / standoils.
  • Oxidized / blown oils.
  • Dehydrated Castor Oil.