An antiozonant, also known as anti-ozonant, is an organic compound that prevents or retards Ozone cracking caused by ozone. The most important antiozonants are those which prevent degradation of like rubber. A number of research projects study the application of another type of antiozonants to protect plants as well as salmonids that are affected by the chemicals.
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. 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,
polybutadiene, styrene-butadiene rubber and
nitrile rubber are the most sensitive to degradation,
[Layer, R. W., & Lattimer, R. P. (1990). Protection of rubber against ozone. Rubber Chemistry and Technology, 63(3), 426-450.] whereas
butyl rubber,
polychloroprene,
EPDM and
Viton are more resistant. Ground-level ozone is naturally present, but it is also a product of
smog and thus degradation is faster in areas of high air pollution. All of these factors make vehicle
tires 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.
[Hans-Wilhelm Engels et al., "Rubber, 4. Chemicals and Additives" in Ullmann's Encyclopedia of Industrial Chemistry, 2007, Wiley-VCH, Weinheim. .]
The most common antiozonants for elastomers are N, N′-substituted p-phenylenediamines (PPD) which can be categorized in three types:
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Dialkyl p-Phenylenediamines, such as N,N'-Di-2-butyl-1,4-phenylenediamine
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Alkyl-aryl p-Phenylenediamines, such as 6PPD
[ 6PPP] or IPPD[ IPPD (product page)]
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Diaryl p-Phenylenediamines, like DPPD
Other classes include:
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Styrenated phenol (SPH), styrenated and alkylated phenol (SAPH)
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Hydrocarbon waxes which create a surface barrier, preventing contact with ozone: paraffin wax, microcrystalline wax.
[ Antioxidants & Antidegradants]
Protection of plants
For the protection of plants like
winter wheat or
maize (EDU) has been used successfully as antiozonant.
See also
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Stabilizer (chemistry)
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Stabilizers for polymers
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Antioxidant
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