__________ is a non volatile film forming constituent of a paint.

ANS:C - Drying oil

Drying oil is a type of oil that has the property of hardening or drying into a solid film when exposed to air. It is a crucial component of oil-based paints and varnishes, providing them with the ability to form a durable, protective coating when applied to surfaces. Here are some key points about drying oils and their role in paints:

1. Composition: Drying oils are typically derived from plants and seeds, such as linseed, tung, walnut, poppy, and safflower oils. These oils contain unsaturated fatty acids, primarily linoleic and linolenic acids, which are prone to oxidation.
2. Oxidation and Polymerization: When drying oils are exposed to air, they undergo a process called oxidation. Oxygen molecules in the air react with the unsaturated fatty acids in the oil, forming peroxides and other reactive intermediates. These intermediates then polymerize, or cross-link, with neighboring molecules, leading to the formation of a solid film.
3. Film Formation: As the drying oil oxidizes and polymerizes, it forms a continuous film that binds together the pigment particles in the paint and adheres them to the surface being painted. This film provides protection against moisture, UV radiation, abrasion, and other environmental factors, enhancing the durability and longevity of the painted surface.
4. Drying Time: The drying time of oil-based paints depends on several factors, including the type of drying oil used, the presence of drying agents or accelerators, and environmental conditions such as temperature and humidity. Some drying oils, such as linseed oil, dry relatively quickly, while others, such as tung oil, may require more time to fully cure.
5. Applications: Drying oils are commonly used in oil-based paints for various applications, including artistic painting, architectural coatings, furniture finishing, and protective coatings for metal surfaces. They are valued for their ability to produce smooth, glossy finishes and for their excellent adhesion and durability.