Effect of crosslink density on the creep behavior of natural rubber vulcanizates

Torsional creep measurements on four natural rubber vulcanizates, crosslinked to different degrees, were carried out in the temperature range from −50 to 90°C. This investigation complements the studies on identical samples of the stress relaxation behavior by Chasset and Thirion and of the dynamic mechanical response by Ferry, Mancke, Maekawa, Ōyanagi, and Dickie. The creep measurements reported are shown to be in agreement with the stress relaxation results. In addition to the usual temperature reduction, a superposed curve was obtained for the long time response using the apparent molecular weight between crosslinks, M c , as a reduction variable. The variation in viscoelastic response with crosslink density is interpreted as a restrictive action of the chemical crosslinks on the transient entanglement network.