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2023

橡胶制品的臭氧老化与保养

当臭氧与橡胶制品接触时，首先与活性双键发生加成反应，生成分子臭氧化物。1分子臭氧酸盐非常不稳定，迅速分解形成羰基2和两性离子。在大多数情况下，两性离子和羰基会重新结合形成有气味的氧化物©,两性离子也可聚合生成过氧化物©或高过氧化物©,此外，当存在甲醇等活性溶剂时，两性离子会与其反应生成甲氧基过氧化氢。臭氧与不饱和橡胶之间反应的活化能很低，反应非常容易进行。反应直到橡胶的双键完全消耗掉为止。此时，橡胶表面形成失去弹性的银白色薄膜。只要没有外力使薄膜破裂，橡胶就不会再继续发生臭氧氧化。如果已经经历过臭氧氧化的橡胶被拉伸或受到动态变形，产生的臭氧氧化膜会开裂，暴露出新的橡胶表面并与臭氧发生反应，导致裂缝继续生长。饱和橡胶不含双键，虽然能与臭氧反应，但反应进行缓慢，不易开裂。
Ozone (O3) in the atmosphere is formed by oxygen molecules absorbing shortwave ultraviolet light from the sun, decomposing oxygen atoms and recombining with oxygen molecules. There is an ozone layer with a concentration of approximately 5X10- in the air at a distance of 20-30km from the Earth's surface. With the vertical flow of air, ozone is brought to the Earth's surface, and the concentration of ozone gradually decreases from high altitude to the ground. In addition, ozone can be generated in areas with concentrated ultraviolet light, discharge areas, and near electric motors, especially in areas where electric sparks are generated. The usual concentration of ozone in the atmosphere is 0-5X10-8. Different regions have different concentrations of ozone; The concentration of ozone varies with different seasons. Although the ozone concentration near the ground is very low, the harm to rubber cannot be ignored.
不饱和橡胶容易发生臭氧氧化及其在臭氧氧化后的外观特性，与热氧老化不同。一是橡胶制品的臭氧氧化只发生在与臭氧接触的表层，整个臭氧氧化过程是从表面到内部; 二是橡胶与臭氧反应形成银白色硬膜 (约lOnm厚)，它可以防止臭氧和橡胶在静态条件下的深度接触。然而，在动态应变条件或静态拉伸条件下，当橡胶的伸长率或拉伸应力超过其临界伸长率或临界应力时，这种薄膜会开裂，使臭氧与新的橡胶表面接触，继续发生臭氧氧化反应并引起裂纹扩展，此外，裂纹出现后，由于应力集中在基部，更容易加深裂纹并形成裂纹。裂纹的方向与应力方向垂直，一般在小应变 (如5%) 下只出现少量裂纹。裂纹方向是可以清楚区分的，但是当橡胶受到多个方向的作用力时，很难区分裂纹方向。
The activation energy of the reaction between ozone and unsaturated rubber is very low, and the reaction is extremely easy to carry out. The reaction occurs until the double bonds of the rubber have been completely consumed, and a silver white film that loses elasticity is formed on the surface of the rubber. As long as there is no external force causing the film to crack, the rubber will no longer continue to undergo ozonation. If the rubber that has already undergone ozone oxidation is stretched or subjected to dynamic deformation, the generated ozone oxidation film will crack, exposing the new rubber surface and reacting with ozone, causing the cracks to continue to grow.
饱和橡胶不含双键，虽然能与臭氧反应，但反应进行缓慢，不易开裂。许多人对不饱和橡胶中气味氧化裂纹的产生和生长进行了研究。这些研究人员根据自己的实验数据提出了裂纹形成和生长的机理。例如，有人认为开裂的发生是由于臭氧氧化物在应力下分解产生的分子链断裂的趋势，导致彼此分离的趋势比重新结合的趋势更大。裂解的生长与臭氧浓度和橡胶分子链的迁移率有关。当臭氧浓度一定时，分子链的迁移率越大，裂纹生长越快。也有人认为，臭氧裂解的产生和生长，与橡胶臭氧氧化形成的臭氧氧化物薄层的物理性质以及与原橡胶表层物理性质的差异有关。例如，专家认为橡胶的臭氧化过程是一个物理和化学同时发生的过程。当橡胶与臭氧接触时，表面的双键迅速与臭氧反应，大多生成臭氧氧化物，使原本光滑的橡胶链迅速转变为含有许多臭氧氧化物环的刚性链。当应力施加到橡胶上时，它会拉伸并展开橡胶链，导致更多的双键与臭氧接触，使橡胶链更脆，并包含更多的臭氧环。脆性表面在应力或动态应力下容易开裂。
Many people have conducted research on the generation and growth of odor oxidation cracking in unsaturated rubber. These researchers have proposed the mechanisms of crack formation and growth based on their own experimental data. For example, some people believe that the occurrence of cracking is due to the tendency of broken molecular chains generated by the decomposition of ozone oxides under stress, resulting in a greater tendency to separate from each other than to recombine. The growth of cracking is related to the concentration of ozone and the mobility of rubber molecular chains. When the ozone concentration is constant, the greater the mobility of the molecular chains, the faster the crack growth. Some people also believe that the generation and growth of ozone cracking are related to the physical properties of the ozone oxide thin layer formed by rubber ozone oxidation and the difference in physical properties from the original rubber surface layer.