Ozone Attack on Rubber Vulcanizates

Abstract

Abstract The effect of the attack of ozone on rubber vulcanizates is well known in a qualitative way. Only recently have efforts been made to study this problem quantitatively. Because of this the state of knowledge on this subject is not so satisfactory as that obtained for ordinary oxidation. A quantitative study of the rate and extent of the reaction of ozone with rubber vulcanizates and the cracking under strain is discussed herein. The general knowledge on this subject tells us that ozone attack results in the cracking of the surface of vulcanizates. Cracking occurs only when the specimen is under some strain during exposure to ozone. The broad quantitative problem then becomes one of defining the factors controlling the reaction while the specific problem relating to cracking becomes one of measuring such crack generation and crack growth in vulcanizates under strain. The method used in this work may be described as follows. A sample is stretched and allowed to relax until most of the pertinent stress relaxation has taken place. Ozone is then admitted to the stretched and relaxed sample. As cracking occurs the stress in the sample decreases and the length increases. The effect of the ozone produced cracks may be considered as related to change in form of work. The initial work done on the sample by stretching is derived from an equation expressing the network-statistical theory of rubber elasticity. The cracking is considered as a transformation of work to form new surface.