An antiozonant, also known as anti-ozonant, is an

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 ...

that prevents or retards damage caused by

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...

. The most important antiozonants are those which prevent degradation of

elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic ...

s like

rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, a ...

. A number of research projects study the application of another type of antiozonats to protect plants.

Effect of ozone

Many elastomers are rich in unsaturated double bonds, which can react with ozone present in the air in process known as

ozonolysis In organic chemistry, ozonolysis is an organic reaction where the unsaturated bonds of alkenes (), alkynes (), or azo compounds () are cleaved with ozone (). Alkenes and alkynes form organic compounds in which the multiple carbon–carbon bon ...

. This reaction breaks the polymer chains, degrading the mechanical properties of the material. The most obvious effect of this is cracking of the elastomer (ozone cracking), which is exacerbated by mechanical stress. The rate of degradation is effected both by the chemical structure of the elastomer and the amount of ozone in the environment. Elastomers which are rich in double bonds, such as

natural rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, a ...

polybutadiene Polybutadiene utadiene rubber BRis a synthetic rubber. Polybutadiene rubber is a polymer formed from the polymerization of the monomer 1,3-butadiene. Polybutadiene has a high resistance to wear and is used especially in the manufacture of ti ...

styrene-butadiene Styrene-butadiene or styrene-butadiene rubber (SBR) describe families of synthetic rubbers derived from styrene and butadiene (the version developed by Goodyear is called Neolite). These materials have good abrasion resistance and good aging st ...

rubber and

nitrile rubber Nitrile rubber, also known as nitrile butadiene rubber, NBR, Buna-N, and acrylonitrile butadiene rubber, is a synthetic rubber derived from acrylonitrile (ACN) and butadiene. Trade names include Perbunan, Nipol, Krynac and Europrene. This rubber is ...

are the most sensitive to degradation, whereas

butyl rubber Butyl rubber, sometimes just called "butyl", is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for isobutylene isoprene rubber. Polyisobutylene, also known as "PIB" or polyisobutene, (C4H8)n, is the ...

polychloroprene Neoprene (also polychloroprene) is a family of synthetic rubbers that are produced by polymerization of chloroprene.Werner Obrecht, Jean-Pierre Lambert, Michael Happ, Christiane Oppenheimer-Stix, John Dunn and Ralf Krüger "Rubber, 4. Emulsion Ru ...

, EPDM and Viton are more resistant.

Ground-level ozone Ground-level ozone (O3), also known as surface-level ozone and tropospheric ozone, is a trace gas in the troposphere (the lowest level of the Earth's atmosphere), with an average concentration of 20–30 parts per billion by volume (ppbv), with cl ...

is naturally present, but it is also a product of

smog Smog, or smoke fog, is a type of intense air pollution. The word "smog" was coined in the early 20th century, and is a portmanteau of the words '' smoke'' and ''fog'' to refer to smoky fog due to its opacity, and odor. The word was then in ...

and thus degradation is faster in areas of high air pollution. All of these factors make vehicle

tires A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface over which t ...

particularly vulnerable, as they contain a high level of unsaturated groups, operate in areas prone to air pollution and are subjected to significant mechanical stresses.

Protection of elastomers

Antiozonants are used as additives in tire manufacturing to retard the effects of ozone. The most common antiozonants for elastomers are ''N'',''N''′-substituted ''p''-phenylenediamines (PPD) which can be categorized in three types: * Dialkyl ''p''-Phenylenediamines, such as

N,N'-Di-2-butyl-1,4-phenylenediamine ''N'',''N''′-Di-2-butyl-1,4-phenylenediamine is an aromatic amine used industrially as an antioxidant to prevent degradation of turbine oils, transformer oils, hydraulic fluids, lubricants, waxes, and greases. It is particularly effective for ...

* Alkyl-aryl ''p''-Phenylenediamines, such as 6PPD or IPPD * Diaryl ''p''-Phenylenediamines, like DPPD Other classes include: * Styrenated phenol (SPH), styrenated and alkylated phenol (SAPH) * Hydrocarbon waxes which create a surface barrier, preventing contact with ozone:

paraffin wax Paraffin wax (or petroleum wax) is a soft colorless solid derived from petroleum, coal, or oil shale that consists of a mixture of hydrocarbon molecules containing between 20 and 40 carbon atoms. It is solid at room temperature and begins to ...

, microcrystalline wax.

Protection of plants

For the protection of plants like

winter wheat Winter wheat (usually '' Triticum aestivum'') are strains of wheat that are planted in the autumn to germinate and develop into young plants that remain in the vegetative phase during the winter and resume growth in early spring. Classification ...

maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn ( North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. ...

Ethylene diurea (EDU) has been used successfully as antiozonant.

References

External links

Review of antiozonants
(TheFreeLibrary) Antioxidants Plastics additives {{organic-compound-stub

Effect of ozone

Protection of elastomers

Protection of plants

See also

References

External links