Linseed Oil - Chemical Aspects

Chemical Aspects

Linseed oil is a triglyceride, like other fats. Linseed oil is distinctive in terms of fatty acid constituents of the triglyceride, which contain an unusually large amount of α-linolenic acid, which has a distinctive reaction toward oxygen in air. Specifically, the constituent fatty acids in a typical linseed oil are of the following types:

• The triply unsaturated α-linolenic acid (51.9-55.2%),
• The saturated acids palmitic acid (about 7%) and stearic acid (3.4-4.6%),
• The monounsaturated oleic acid (18.5-22.6%),
• The doubly unsaturated linoleic acid (14.2-17%).

Having a high content of di- and triunsaturated esters, linseed oil is particularly susceptible to polymerization reactions upon exposure to oxygen in air. This polymerization, which is called "drying," results in the rigidification of the material. The drying process can be so exothermic as to pose a fire hazard under certain circumstances. To prevent premature drying, linseed oil-based products (oil paints, putty) should be stored in air-tight containers.