Resin

A resin is a solid or very thick liquid that can be turned into a polymer. Resins come from plants and are made of special mixtures of organic compounds, mostly terpenes. They are different from gums, which dissolve in water.

Common resins include pine oleoresins, amber, frankincense, myrrh, and shellac, which comes from animals. People use resins to make varnishes, adhesives, food additives, incenses, and perfumes.

Resins help protect plants from insects and diseases. When a plant is hurt, it makes resin to push away harmful creatures. The special smells in resin can even bring helpful insects that protect the plant.

Composition

Most plant resins are made of special plant compounds called terpenes. Some important ones are α-pinene, β-pinene, 3-carene, and sabinene. Other types include limonene and terpinolene. Some resins also have things called resin acids.

Rosin is a type of hardened resin with some parts removed. It is usually clear or slightly yellow and can melt when heated. Rosin comes from pine trees and some other plants. An example of a resin from insects is shellac.

History and etymology

People have used plant resins for a very long time. Writers in ancient Greece like Theophrastus and in ancient Rome like Pliny the Elder wrote about them. Two important resins were frankincense and myrrh, which were very valuable in ancient Egypt and used in special religious ceremonies.

The word "resin" comes from the French word resine, which itself comes from the Latin resina. This Latin word is related to the Greek word ῥητίνη rhētínē, meaning "resin of the pine". Today, we use the word "resin" for many liquids that harden into a shiny finish, like nail polish. There are also special kinds of resins made by people, such as epoxy resin.

Some natural resins mixed with oils are called oleoresins. Others that contain certain acids are called balsams. These natural resins are sometimes used in perfumes.

Other liquids from plants, like sap, latex, or mucilage, are different from resins and have other jobs in the plant.

Uses

Plant resins are used to make varnishes, adhesives, and food glazing agents. They are also used to make incense and perfume. One of the oldest uses of plant resin was as an adhesive for attaching stone tools, found in Southern Africa.

Hard, clear resins such as copals, dammars, mastic, and sandarac are mainly used for varnishes and adhesives. Softer, scented resins like frankincense, elemi, turpentine, and copaiba, as well as gum resins with essential oils like ammoniacum, asafoetida, gamboge, myrrh, and scammony, are often used for food flavoring and incense. The resin from the Aleppo pine is used to give flavor to retsina, a special Greek resinated wine.

Animal resins, though less common than plant or synthetic resins, are sometimes used. For example, lac from Kerria lacca is used for sealing wax in India and for lacquerware in Sri Lanka.

Synthetic resins

Main article: Synthetic resin

Many materials come from changing synthetic resins into solids. For example, bisphenol A diglycidyl ether becomes epoxy glue when mixed with a hardener. Silicones are made from silicone resins. Alkyd resins are used in paints and varnishes and harden when exposed to oxygen in the air.