Ozone aging of rubber flexible joints is a surface reaction, and the reaction attempt on the surface of unstressed rubber is 10-40 molecules thick, or (10~50)10-6 times mm thick. When unstressed rubber is exposed to O3, the rubber reacts with O3 until the double bond on the surface is completely reacted and terminated, forming a hard gray brittle film similar to spray frost on the surface, making it lose its luster. When the stretched rubber is subjected to ozone aging, the surface is subjected to ozone cracking, but it is believed through research that there is a critical stress for ozone cracking of rubber, and when the elongation or stress of rubber is lower than the critical value, it will not produce cracking when ozone aging occurs, which is an inherent characteristic of rubber.
The direction of cracking is perpendicular to the direction of stress when ozone cracking is produced in rubber flexible joints, which is different from the cracking caused by ozone cracking and photo-oxidative aging, and it should be noted that when ozone aging is produced in rubber subjected to stress in multiple directions, it is difficult to see the direction of ozone cracking, which is similar to the cracking produced by photo-oxidative aging.
