Alkyd is a polyester resin used in some paints, resins, and clear coatings to form a film. It is synthetic polyester, which the addition of fatty acids and oils modifies. The word alkyd is a combination of “alcohol” and “acid.” Alkyds stem from a polymerization reaction between an alcohol and an acid or anhydride. The addition of unsaturated oil to the ester-forming compounds creates branched polyester with fatty-acid side groups, otherwise known as alkyd.  Read More

Development of Alkyds
To create alkyds, scientists use the condensation from the reaction between fatty acids, dibasic acids, and polyols. The fatty acid is a renewable resource, and it stems from vegetable matter such as linseed oil, tung oil, or castor oil. The most common elements involved in the development of alkyd are glycerol, trimethylolpropane, and pentaerythritol for polyols.

The type of oil used in a formulation has a major impact on the alkyd’s drying capabilities. There are drying, semidrying, and non-drying fatty acids for use in alkyds. To determine the drying index, add the percentage of linolenic acid to two times the percentage of linoleic acid. If the answer is greater than 70, the non-conjugated oil is a “drying oil.” The alkyd has better drying ability the higher the percentage of linolenic. However, the rate of yellowing in the dry resin also increases. Using sunflower and safflower oils in alkyds can increase drying speed while combating yellowing.

Alkyd Uses
The most common place where alkyd resin technology is used is in paints and resins. Alkyd paints dry faster than oil-based paints. They are typically dry to the touch within 12 to 48 hours. Alkyd coatings, on the other hand, may be slower to dry than urethane coatings. Alkyd coatings do not have added hardeners but instead consist of only one component. Alkyd coatings use a cross-linking reaction with oxygen to provide a tack-free film after the paint is dried.

There are many different versions of alkyds depending on the elements used in its creation. Some alkyds hold up well in water, while others are more sensitive to external factors. One can use alkyd paints and resins for a variety of applications, especially those in need of high durability and resistance to wear over time. Alkyd paints are preferable for high-traffic applications such as in hallways, kitchens, and bathrooms.

Alkyd paints are resistant to discoloration, moisture, and humidity. They are also very easy to clean. Using alkyd paint will result in a sheen that lasts for the long run. Applying thin coats of alkyd paints is better than heavy coats, as this practice will improve dry time. You may apply alkyd paint over latex paint, but not vice versa. The glossy finish of alkyd paint makes it difficult for latex paint to adhere to the surface.

Summary
Alkyd paints are not as popular as they once were due to issues relating to environmental friendliness. Alkyds paints use chemical solvents and emit toxic Volatile Organic Compounds (VOCs) that latex paints do not. When using alkyd substances, ensure adequate ventilation and use proper safety gear.  Read Less