Effect of Oxygen on the Tear Strength of Elastomers.

摘要

Rates of tearing under steady and intermittent loads have been measured for some representative elastomers. The rate depended strongly upon the load and also upon the environment. Tearing was strongly upon the load and also upon the environment. Tearing was much slower for SBR and BR vulcanizates in vacuo, especially at low loads, by a factor of up to 10X. For NR the effect was quite small by a factor of 2X at the most. Experiments were also carried out in the presence of thiophenol vapor, a radical trap. For NR, the effect was found only at high loads, when tearing was much slower, by a factor of about 10X. The improvement persisted after thiophenol was removed it is attributed chemical modification of the vulcanizate. On the other hand, tearing of SBR was accelerated at all loads by thiophenol vapor, to the same degree as in air. Much smaller effects were found for a peroxide vulcanizate off SBR. It is concluded that the reactions of sulfur crosslinks with radical acceptors, including oxygen, lead to an increased rate of tearing in SBR. For BR and NR vulcanizates the situation is less clear, because of the smaller effect of oxygen in the first case and of thiophenol in the second. Keywords: Fatigue; Crack growth. (KR)