Antiozonant mechanisms combinations

Chemical antiozonants have been developed to protect rubber against ozone under such dynamic conditions. Several mechanisms have been proposed to explain how chemical antiozonants protect rubber. The scavenging mechanism, the protective film mechanism, or a combination of both are nowadays the most accepted mechanisms. 

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... 

Of auxiliary agents, linseed oil, nnsatnrated vegetable oils, rapeseed oil, and hydrocarbon waxes enhance the efficiency of an antiozonant in a dynamic ozone test as they bloom to the snrface of the pol5mier. Ester plasticizers snch as dioctyl sebacate impair ozone resistance presnmably becanse of enhanced solnbility of polar esters in the polar polychloroprene network polymer. Finally, the mechanism for ozone attack differs appreciably from oxygen attack at allylic atoms. Thus, an antioxidant is generally nsed in combination with an antiozonant for polychloroprene. 

Substitutes for wax to provide protection of tyre sidewalls against static ozone cracking are examined. The use of low levels of wax or its complete elimination in the tyre sidewall by combinations with dialkyl paraphenylene diamine (77PD) or 2,4,6-tris - (N-1,4 dimethyl pentyl-p-phenylene diamino) 1, 3, 5 triazine (TAPDT) is discussed for the long term resistance to dynamic ozone crack resistance. In addition, a mechanism is proposed to explain how ozone reacts with antiozonants, which involves a scavenging function. 5 refs. 

In conclusion, the selection of the proper antidegradants for elastomeric compounds should be based upon a carefiil assessment of the elastomers used, the normal service requirements expected from these compounds, and the environment in which they are to perform. Only then, one can choose the ideal combination of antioxidants and antiozonants. It must be emphasized that the degradation of elastomers proceeds via several mechanisms, and as a result, it is essential to choose and use a combination of antidegradants which will inhibit aU of the described mechanisms of degradation that are expected to be encountered during a products service fife [28]. 

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