Static Exposure Testing of Automotive Compounds

Abstract

Abstract Deterioration of rubber products on outdoor exposure is due to the action of sunlight and ozone. Ozone cracking results when rubber is exposed under strain. The type of cracking produced by ozone is not produced by other elements or materials normally present in the atmosphere. Light-energized oxidation produces a crazed condition on the surface of the rubber, which is quite different from the effects produced by ozone. This study was undertaken to determine the factors which influence the resistance of rubber products to ozone. It was found that rubber cured under strain cracks faster than when cured at rest. Manufacturing defects, such as blisters, air traps, foreign matter, and pigment agglomerates, resulted in premature cracking. Certain manganese, copper, and iron salts had an adverse effect on ozone resistance in outdoor and accelerated exposure tests. Some dispersing agents used to make carbon black slurries for GR-S carbon black masterbatches, showed an adverse effect on weather aging. The selection of a polymer, such as natural rubber, GR-S, Neoprene, or Butyl rubber, has a marked influence on the ozone resistance of automotive rubber products. Unless a polymer is handled and compounded properly, good ozone resistance is not obtained. In outdoor exposure the effect of sunlight, ozone, heat, and water varies seasonally in Florida, California, Michigan, and Illinois. Many tests and much good judgment must be exercised in correlating accelerated and outdoor exposure tests.