Thermal Oxidation of Cured Rubbers

The aging of cured rubbers, as has already been mentioned, differs substantially from the aging of the raw rubbers, on the basis of which they were prepared. 

The method of vulcanization of cured rubbers using thiuram disulfides, in the absence of elementary sulfur, is widely used in the rubber industry. The basic advantage of thiuram rubbers is their high resistance to thermal aging. Thus, for example, cured rubbers based on butadiene nitrile rubbers, vulcanized with thiuram, manifest ability to work at 150-180°C, while the temperature limit of the operation of sulfur rubbers does not exceed 100-110°C. 

It has been established that the cause of the high thermal stability of the indicated cured rubbers is the presence of zinc dithiocarbamates, which are formed from dithiocarbamic acid (one of the decomposition products of thiuram disulfide) and zinc oxide. 

As is shown in F . 172 [24], vulcanizates obtained without zinc oxide exhibit no induction period in oxidation. 

In a study of the inhibiting ability of dithiocarbamates containing various cations, as well as other radicals on the nitrogen atom, it was found that the most effective are the dithiocarbamates of Zn, Cu, and Bi (Fig. 173). 

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