Ozone degradation antiozonants

Ai,Af-Disubstituted- -phenylenediamines, such as A/-phenyl-Af -(l,3-dimethylbutyl)-/)-phenylenediamine [793-24-8] (10), are used in greater quantities than other classes of antioxidants. These products protect unsaturated elastomers against oxidation as well as ozone degradation (see Antiozonants). 

Antiozonant additives are employed with unsaturated rubbers such as natural rubber, nitrile rubber, styrene-butadiene rubber, etc., to minimise the atmospheric ozone degradation reaction. Common antiozonant types include the parapheny-lene diamines such as N-(l,3-dimethylbutyl)-AT-phenyl-p-phenylene diamine (6PPD) and N-isopropyl-N7 phenyl-p-phenylene diamine (IPPD). Both these antioxidants can be identified and quantified using GC- or LC-based techniques. 

PEROXIDES AND PEROXIDE COMPOUNDS - ORGANIC PEROXIDES] (Vol 18) -from ozone degradation ofrubber [ANTIOZONANTS] (Vol 3)... 

A government-sponsored research program led to the discovery of chemicals that prevented ozone cracking when added to rubber compounds. Commercial antiozonants have been available since the early 1950s. Since that time, the ozone degradation problem has worsened as atmospheric ozone concentrations have gradually increased, especially in urban industrial areas. 

The PPD class of antidegradants provides by far the best antiozonant protection (for a review of antiozonants, see Reference 82). PPDs inhibit ozone degradation of rubber by multiple mechanisms (76,83-85) ... 

Environmental Impact of Ambient Ozone. Ozone can be toxic to plants, animals, and fish. The lethal dose, LD q, for albino mice is 3.8 ppmv for a 4-h exposure (156) the 96-h LC q for striped bass, channel catfish, and rainbow trout is 80, 30, and 9.3 ppb, respectively. Small, natural, and anthropogenic atmospheric ozone concentrations can increase the weathering and aging of materials such as plastics, paint, textiles, and mbber. For example, mbber is degraded by reaction of ozone with carbon—carbon double bonds of the mbber polymer, requiring the addition of aromatic amines as ozone scavengers (see Antioxidants Antiozonants). An ozone decomposing polymer (noXon) has been developed that destroys ozone in air or water (157). 

Antiozonants (qv) prevent or reduce polymer degradation by the active ozone molecule. Some antioxidant compounds, such as the /)i7n7-phenylenediamines, are excellent as antiozonants (36). The protection by these compounds is thought to be either a reaction with the ozone before it can react with the surface of the mbber or an aid in reuniting chains severed by ozone (37). 

Since the mid-1950s several materials have been found effective in combating ozone-initiated degradation, in particular certain p-phenylenediamine derivatives. The actual choice of such antiozonants depends on the type of polymer and on whether or not the polymer is to be subject to dynamic stressing in service. Since antiozonants are not known to have any use in plastics materials, even those which may have certain rubber particles for toughening, they will not be dealt with further here. Anyone interested further should consult references 3-5. 

The heat and ozone resistant [126] EPR was made by incorporating acrylic rubber, dicumyl peroxide, triaUyl cyanurate, ZnO and carbon-black into the matrix. Triallyl cyanurate increases the crosslinking efficiency probably due to an addition reaction between polymeric and aUyl radicals and leads to stable chemical crosslinks. Thus ozone because there is no unsaturation cannot initiate a degradation reaction. Digteva et al. [127] prepared sealants for use at high temperature by adding aromatic diaminodisulfide, MgO, ZnO and carbon black in EPR. The aromatic diaminodisulfide is an antiozonant and functions both as an antioxidant and a... 

The mechanism of the antiozonant protection has been the matter of studies and discussions for a long time [3,4,18,21,31] and it is still an area of active research. Due to the diversity of the deteriogens and reactive products of rubber degradation involved in ozone ageing, more concerted protective mechanisms are certainly included [247], The antiozonant activity accounts for a combination of a direct scavenging of ozone by the chemical AOZ and formation of... 

The unsaturated nature of an elastomer accounts for its unique viscoelastic properties. However, the presence of carbon-carbon double bonds renders elastomers susceptible to attack by oxygen, ozone, and thermal degradation. A comprehensive review of elastomer oxidation and the role of antioxidants and antiozonants is available (Hong, 2004). 

Paraffin waxes ethylene diurea (EDU) p-phenylenedi-amines, etc. Antiozonants Antiozonants prevent or slow down the degradation of material caused by ozone gas in the air. For example, paraffin waxes form a surface barrier for ozone... 

Antioxidants/ antiozonants 0-7 Inhibit attack by oxygen and ozone. Improve flex fatigue and inhibit the degradation effects of metal impurities... 

The shortcomings of NR include its service temperature, from —18 to 120°C ( — 6 to 248 F). Its poor oil, oxidation, and ozone resistance can be minimized either by proper design accommodation or by compounding. Degradation from such environments is essentially a surface effect that can be tolerated or minimized by using thicker cross-sections, shielding, or adding antioxidants and antiozonants. 

The substituted PPDs, described above, are used as ehemieal antiozonants when service conditions involve eontinuous dynamie deformation. For a particular rubber, the optimum PPD is one which is soluble in the elastomer, and which will diffuse to the produet surface as needed. At the surface, a protective film is formed by the reaction between ozone and the PPD. The ability of the PPD to migrate to the surface as this film is degraded or otherwise broken, and thus react with ozone to repair it, is essential to long term protection. The alkylaryl PPDs are the most widely used for their protection against both oxidation and ozone. 

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