Linseed Oil
Linseed oil, also known as flaxseed oil, comes from the seeds of the flax plant, Linum usitatissimum. This oil was the main binding agent used in paints prior to the adoption of synthetic compounds. Linseed oil consists of triglycerides of mainly unsaturated fatty acids. The approximate composition is shown in the following table.
| Description | Emperical Formula/Structural Formula | Carbon Bond Configuration | Percent (%) |
|---|---|---|---|
| saturated acids | CnH2nO2 CH3(CH2)4CO2H |
saturated | 5 |
| oleic acid | C18H34O2 CH3(CH2)7CH=CH(CH2)7CO2H |
one double bond | 15 |
| linoleic acid | C18H32O2 CH3(CH2)3(CH2CH=CH)2(CH2)7CO2H |
two isolated double bonds | 45 |
| linolenic acid | C18H30O2 CH3(CH2CH=CH)3(CH2)7CO2H |
three isolated double bonds | 35 |
Omega-3 and Omega-6 Fatty Acids
Omega-3 and Omega-6 fatty acids are important in human nutrition. The term Omega refers to the end of the molecule where the methyl (CH3) group is located. The numerical designation refers to the carbon atom on which the first double bond is located. In linolenic acid this is the third carbon atom, so linolenic acid is an Omega-3 fatty acid. In linoleic acid this is the sixth carbon atom, so linoleic acid is an Omega-6 fatty acid.
Linseed Oil and the Paint Industry
Linseed oil is the most important naturally occuring oil used by the paint industry. Uses include house paints, sealers, primers, enamels, and varnishes. It is supplied in more grades than any other oil, as described in the following list:
- Improved raw. This grade does not "break" (precipitate proteins and
phosphatides) at any temperature. It is used to produce linoleate driers, as a
pigment grinding oil, and in less expensive varnishes.
Note: A linoleate drier is an oil drying agent based on the salts of lead, maganese, or cobalt and, originally, the fatty acids from linseed oil or rosin.
- Non-break. Similar to improved raw but with fewer free fatty acids (lower acid number).
- Alkali refined. The alkali refining results in an oil with a neutral pH. It is used in varnishes and high-grade house paints.
- Acid refined. Used for pigment grinding because of its outstanding wetting properties.
- Boiled. The oil is not actually boiled, but heated to a high temperature to incorporate drying agents. It is typically added to paste or house paints to bring them to the required oil content.
- Heat bodied. Made by heating alkali refined linseed oil until the desired body is achieved. Typically heating temperatures are between 550o and 600o F.
- Blown. The oil is bodied by having air blown through it as it is heated. Do to partial oxidation, this grade dries faster than any other grade of linseed oil and has outstanding flow and gloss properties.