Preliminary study of stress aided photodegradation of rubber

A study has been made of the photodegradation of a car tyre sidewall rubber exposed to ultraviolet irradiation while under tensile stress. Comparisons are made of the behaviour of the unprotected rubber; the rubber filled with carbon black; the rubber modified by the inclusion of an antioxidant; and the rubber containing both carbon black and antioxidant. All four materials showed similar stages on the way towards catastrophic cracking; both carbon black and antioxidant slowed the progress very considerably and the presence of both reduced the rate of degradation still further but did not eliminate it altogether. Tensile stress accelerated degradation. Tests were conducted at 30 and 50°C and at various applied stresses. From the limited number of stress- temperature combinations tested, an attempt was made to conduct an approximate analysis using the Zhurkov equation to obtain activation volumes for the process. The activation volumes obtained seemed to be insensitive to the presence of antioxidant and for rubber containing no carbon black were ∼4 nm 3 whereas for the carbon black filled samples the value was close to 0·75 nm 3