Effect of carbon black content on the stress relaxation of natural rubber

In several applications of rubbers and rubber compounds – such as tires – product performance is largely determined by material hysteretic behaviour and strength, which are in turn related to reversible and irreversible phenomena occurring at large strains. Among these phenomena, the strain‐induced crystallization may be significant. In order to investigate this phenomenon, stress relaxation tests have been widely adopted on unfilled rubber both at low [1-3] and room temperature [3-5]. More in general, this kind of test has been also performed on filled rubber compounds in order to relate the time dependent mechanical behaviour to the structural modification of the material [6-7]. In this work a systematic study on the relaxation behaviour of natural rubber compounds differing in carbon black content is performed and a correlation between the obtained results and changes in rubber microstructure is investigated.