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It is a known fact that the mechanical properties of rubber depend essentially upon the density (i.e., the crosslink density) of the vulcanization network. The dependence of the “equilibrium” (statistical) modulus of elasticity upon the concentration of crosslinks as well as the dependence of the tensile strength —has been studied in a series of investigations. In contrast to this, analogous investigations of the dynamic mechanical characteristics are practically nonexistent. We have undertaken our present work with the hope of filling this gap. Series of gum compounds were prepared from natural (smoked sheet) and synthetic polyisoprene (SKI), sodium butadiene (SKB), butadiene-styrene (SKS-30A), and butadiene-nitrile (SKN-26) rubbers which varied in their degree of vulcanization. The percentage of sulfur and accelerator were varied as were the temperature and the time of vulcanization. The mechanical-dynamic characteristics of the rubber at a predetermined impact pressure—the rebound elasticity and the dynamic elastic modulus were studied with the pendulum elastometer KS over a temperature range of 20–100° C. The duration of the stress was .03/.05 second. We estimated the concentration of crosslinks in the rubber samples from the magnitude of the equilibrium modulus. In order to determine this characteristic, we compressed specimens which were 20 mm in height and 10 mm in diameter 15% and studied the relaxation of stress. The specimens were also tested on the pendulum elastometer. Heppler's consistometer operating on the lever weight principle, was adapted for our measurements. The experiments were conducted at 60° C, the thermostatic control being effected with the help of Heppler's ultrathermostat.

The authors investigated the abrasion of a number of vulcanized rubbers with the sliding of a smooth steel indenter. Abrasion was achieved by repeated action of an indenter, moving reciprocally along one and the same portion of the surface of the rubber. In the surface layer being destroyed the rubber became tacky; the removal of rubber in abrasion took place by the rolling up into “rolls” of the altered (sticky) surface layer. The character of destruction of the rubber in abrasion is affected by the type of the original rubber, and, in some cases, by the presence of oxygen in the atmosphere. The process of abrasion of vulcanizates of natural rubber and SKI is accompanied by perceptible oxidative degradation. Evidently the wear of rubber is linked essentially with the development of mechanochemical degradative processes.

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