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In polymer chemistry and materials science, resin is a
solid Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structur ...
or highly
viscous The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the in ...
substance of plant or synthetic origin that is typically convertible into
polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
s. Resins are usually mixtures of
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s. This article focuses on naturally occurring resins. Plants secrete resins for their protective benefits in response to injury. The resin protects the plant from insects and pathogens. Resins confound a wide range of herbivores, insects, and pathogens, while the volatile
phenolic compounds In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (— O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are c ...
may attract benefactors such as parasitoids or predators of the herbivores that attack the plant.


Composition

Most plant resins are composed of terpenes. Specific components are alpha-pinene, beta-pinene, delta-3 carene, and sabinene, the monocyclic terpenes limonene and terpinolene, and smaller amounts of the tricyclic
sesquiterpene Sesquiterpenes are a class of terpenes that consist of three isoprene units and often have the molecular formula C15H24. Like monoterpenes, sesquiterpenes may be cyclic or contain rings, including many unique combinations. Biochemical modific ...
s,
longifolene Longifolene is the common (or trivial) chemical name of a naturally occurring, oily liquid hydrocarbon found primarily in the high-boiling fraction of certain pine resins. The name is derived from that of a pine species from which the compound ...
, caryophyllene, and delta-cadinene. Some resins also contain a high proportion of
resin acid Resin acid refers to mixtures of several related carboxylic acids, primarily abietic acid, found in tree resins. Nearly all resin acids have the same basic skeleton: three fused rings having the empirical formula C19H29COOH. Resin acids are tack ...
s. Rosins on the other hand are less volatile and consist of diterpenes among other compounds.


Examples

Examples of plant resins include amber, Balm of Gilead, balsam, Canada balsam, copal from trees of '' Protium copal'' and '' Hymenaea courbaril'', dammar gum from trees of the family Dipterocarpaceae,
dragon's blood Dragon's blood is a bright red resin which is obtained from different species of a number of distinct plant genera: '' Calamus'' spp. (previously ''Daemonorops'') also including '' Calamus rotang'', '' Croton'', '' Dracaena'' and ''Pterocarpus'' ...
from the dragon trees ('' Dracaena'' species),
elemi ''Canarium luzonicum'', commonly known as elemi, is a tree native to the Philippines. The oleoresin harvested from it is also known as elemi. Synonyms * ''Canarium carapifolium'' G.Perkins * ''Canarium oliganthum'' Merr. * ''Canarium polyanth ...
, frankincense from '' Boswellia sacra'', galbanum from ''
Ferula gummosa ''Ferula gummosa'' is a perennial herb of ''Ferula'' in the family Apiaceae. It is native to Iran and Turkmenistan. Its gum resin is called galbanum Galbanum is an aromatic gum resin and a product of certain umbelliferous Persian plant spe ...
'', gum guaiacum from the lignum vitae trees of the genus ''
Guaiacum ''Guaiacum'' (''OED'' 2nd edition, 1989.Entry "guaiacum"
in
kauri gum from trees of '' Agathis australis'', hashish (Cannabis resin) from '' Cannabis indica'', labdanum from mediterranean species of ''
Cistus ''Cistus'' (from the Greek ''kistos'') is a genus of flowering plants in the rockrose family Cistaceae, containing about 20 species (Ellul ''et al.'' 2002). They are perennial shrubs found on dry or rocky soils throughout the Mediterranean region ...
'', mastic (plant resin) from the mastic tree '' Pistacia lentiscus'', myrrh from shrubs of '' Commiphora'', sandarac resin from ''
Tetraclinis articulata ''Tetraclinis'' (also called arar, araar or Sictus tree) is a genus of evergreen coniferous trees in the cypress family Cupressaceae, containing only one species, ''Tetraclinis articulata'', also known as Thuja articulata,styrax (a
Benzoin resin Benzoin or benjamin (corrupted pronunciation) is a balsamic resin obtained from the bark of several species of trees in the genus '' Styrax''. It is used in perfumes and some kinds of incense and as a flavoring and medicine (see tincture of b ...
from various '' Styrax'' species) and spinifex resin from Australian grasses. Amber is
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
resin (also called resinite) from coniferous and other tree species. Copal, kauri gum, dammar and other resins may also be found as subfossil deposits. Subfossil copal can be distinguished from genuine fossil amber because it becomes tacky when a drop of a solvent such as
acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscibl ...
or chloroform is placed on it. African copal and the kauri gum of New Zealand are also procured in a semi-fossil condition.


Rosin

Rosin is a solidified resin from which the volatile
terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n > 1. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes ...
s have been removed by distillation. Typical rosin is a transparent or translucent mass, with a vitreous fracture and a faintly yellow or brown colour, non-odorous or having only a slight turpentine odour and taste. Rosin is insoluble in water, mostly soluble in alcohol, essential oils,
ether In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again ...
, and hot fatty oils. Rosin softens and melts when heated and burns with a bright but smoky flame. Rosin consists of a complex mixture of different substances including organic acids named the
resin acid Resin acid refers to mixtures of several related carboxylic acids, primarily abietic acid, found in tree resins. Nearly all resin acids have the same basic skeleton: three fused rings having the empirical formula C19H29COOH. Resin acids are tack ...
s. Related to the terpenes, resin acid is
oxidized Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
terpenes. Resin acids dissolve in alkalis to form resin soaps, from which the resin acids are regenerated upon treatment with acids. Examples of resin acids are
abietic acid Abietic acid (also known as ''abietinic acid'' or ''sylvic acid'') is an organic compound that occurs widely in trees. It is the primary component of resin acid, is the primary irritant in pine wood and resin, isolated from rosin (via isomerizat ...
(sylvic acid), C20H30O2,
plicatic acid Plicatic acid is a carboxylic acid from the resin acid group. It is naturally found in ''Thuja'' and cypress resin. It is the main irritant and contact allergen present in thuja wood. (''Cf.'' pine, where the primary irritant is abietic acid.) ...
contained in cedar, and pimaric acid, C20H30O2, a constituent of galipot resin. Abietic acid can also be extracted from rosin by means of hot alcohol. Pimaric acid closely resembles abietic acid into which it passes when distilled in a vacuum; it has been supposed to consist of three isomers. Rosin is obtained from pines and some other
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...
s, mostly conifers. Plant resins are generally produced as stem secretions, but in some Central and South American species of ''
Dalechampia ''Dalechampia'' is a genus of plant of the family Euphorbiaceae and of the monogeneric subtribe Dalechampiinae. It is widespread across lowland tropical areas (generally below 2,000 m ASL) primarily in the Americas with smaller numbers of spe ...
'' and '' Clusia'' they are produced as pollination rewards, and used by some stingless bee species in nest construction. Propolis, consisting largely of resins collected from plants such as poplars and conifers, is used by honey bees to seal small gaps in their hives, while larger gaps are filled with beeswax.


Petroleum- and insect-derived resins

Shellac is an example of an insect-derived resin. Asphaltite and Utah resin are petroleum bitumens.


History and etymology

Human use of plant resins has a very long history that was documented in
ancient Greece Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cu ...
by Theophrastus, in ancient Rome by Pliny the Elder, and especially in the resins known as frankincense and myrrh, prized in ancient Egypt. These were highly prized substances, and required as incense in some religious rites. The word ''resin'' comes from French ''resine'', from Latin ''resina'' "resin", which either derives from or is a cognate of the Greek ''rhētínē'' "resin of the pine", of unknown earlier origin, though probably non-
Indo-European The Indo-European languages are a language family native to the overwhelming majority of Europe, the Iranian plateau, and the northern Indian subcontinent. Some European languages of this family, English, French, Portuguese, Russian, Du ...
. The word "resin" has been applied in the modern world to nearly any component of a liquid that will set into a hard lacquer or enamel-like finish. An example is nail polish. Certain "casting resins" and synthetic resins (such as epoxy resin) have also been given the name "resin". Some naturally-derived resins, when soft, are known as 'oleoresins', and when containing
benzoic acid Benzoic acid is a white (or colorless) solid organic compound with the formula , whose structure consists of a benzene ring () with a carboxyl () substituent. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin ...
or cinnamic acid they are called balsams. Oleoresins are naturally-occurring mixtures of an oil and a resin; they can be extracted from various plants. Other resinous products in their natural condition are a mix with gum or mucilaginous substances and known as gum resins. Several natural resins are used as ingredients in perfumes, e.g., balsams of Peru and tolu, elemi, styrax, and certain turpentines.


Non-resinous exudates

Other liquid compounds found inside plants or exuded by plants, such as sap, latex, or mucilage, are sometimes confused with resin but are not the same. Saps, in particular, serve a nutritive function that resins do not.


Uses


Plant resins

Plant resins are valued for the production of varnishes, adhesives, and food
glazing agent A glazing agent is a natural or synthetic substance that provides a waxy, homogeneous, coating to prevent water loss from a surface and provide other protection. Natural Natural glazing agents keep moisture inside plants and insects. Scientists ...
s. They are also prized as raw materials for the synthesis of other organic compounds and provide constituents of incense and
perfume Perfume (, ; french: parfum) is a mixture of fragrant essential oils or aroma compounds (fragrances), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and living-spaces an agreeable scent ...
. The oldest known use of plant resin comes from the late Middle Stone Age in Southern Africa where it was used as an adhesive for hafting stone tools. The hard transparent resins, such as the copals, dammars, mastic, and sandarac, are principally used for varnishes and adhesives, while the softer odoriferous oleo-resins ( frankincense,
elemi ''Canarium luzonicum'', commonly known as elemi, is a tree native to the Philippines. The oleoresin harvested from it is also known as elemi. Synonyms * ''Canarium carapifolium'' G.Perkins * ''Canarium oliganthum'' Merr. * ''Canarium polyanth ...
,
turpentine Turpentine (which is also called spirit of turpentine, oil of turpentine, terebenthene, terebinthine and (colloquially) turps) is a fluid obtained by the distillation of resin harvested from living trees, mainly pines. Mainly used as a special ...
,
copaiba Copaiba is a stimulant oleoresin obtained from the trunk of several pinnate-leaved South American leguminous trees (genus ''Copaifera''). The thick, transparent exudate varies in color from light gold to dark brown, depending on the ratio of resi ...
), and gum resins containing essential oils ( ammoniacum, asafoetida, gamboge, myrrh, and scammony) are more used for therapeutic purposes, food and incense. The resin of the Aleppo Pine is used to flavour retsina, a Greek resinated wine.


Synthetic resins

Many materials are produced via the conversion of synthetic resins to solids. Important examples are bisphenol A diglycidyl ether, which is a resin converted to
epoxy glue Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also c ...
upon the addition of a hardener. Silicones are often prepared from silicone resins via room temperature vulcanization. Alkyd resins are used in paints and varnishes and harden or cure by exposure to
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
in the air.


See also

* Amber * Resin extraction – method of harvesting resin from trees * Balsam of Peru – a balsam used in food and drink for flavoring, in perfumes and toiletries for fragrance, and in medicine and pharmaceutical items. * Mastic (plant resin) – resin from the Pistacia lentiscus tree * Pitch (resin) * Kino (gum) – a plant gum similar to resin * Biodegradable – plant resins are naturally biodegradable in many circumstances. * Resin casting – casting with a resin, usually using a synthetic not a natural resin. *
Polyresin Polyester resins are synthetic resins formed by the reaction of dibasic organic acids and polyhydric alcohols. Maleic anhydride is a commonly used raw material with diacid functionality in unsaturated polyester resins. Unsaturated polyester resi ...
– a hard, synthetic resin for casting in molds


References


External links

* * {{Authority control Non-timber forest products Papermaking Tree tapping