Changes in tensile and tearing fracture properties of carbon-black filled rubber vulcanizates by thermal aging

The effects of thermal aging on the tensile and tearing fracture properties of carbon-black (CB)-filled natural rubber vulcanizates were tested and analyzed. The specimens were subjected to thermo-oxidative aging at 100 degrees C and 120 degrees C, respectively, for various periods of time ranging from 10 to 168hr and then mechanically stretched to fracture by tension or tearing with a 5943 Instron single column materials testing system. The elastic modulus, tensile strength, stretch to fracture, and tearing strength of the aged specimens were measured as a function of aged time at each aging temperature. The experimental results demonstrated that the neo-Hookean hyperelastic model is applicable to describe the tensile stress-stretch behavior of CB-filled rubbers when the stretch is small comparing with the extension limit. Moreover, the elastic modulus increases as the aged time increases, while the tensile strength, the stretch to fracture, and the tearing strength decreases with the aged time. Meanwhile, the crosslink density increased in a same trend with the elastic modulus as the elastic modulus is linearly proportional to the crosslink density of the rubber material, no matter what mechanism under which the crosslink density is affected, like CB loading or aged time. The change in mechanical properties of the filled rubbers due to thermal aging is found to be dependent on the aging temperature and the CB loading, and the higher the aging temperature and the CB loading, the more pronounced the change in mechanical properties. Copyright (c) 2015 John Wiley & Sons, Ltd.