A survey has been made of hard GR-S with regard to sulfur requirement and effects of various pigments, softeners, and accelerators on tensile strength, ultimate elongation, hardness, and stiffness. Of particular interest where the observations that hard GR-S had a higher tensile strength than hard Hevea rubber, and that hard GR-S did not undergo much loss in tensile strength when compounded with 60 volumes of channel black or semi-reinforcing black.

The authors believe that the tear resistance data presented in this paper should be kept in mind by anyone contemplating the use of Buna-S in applications where occasional contact with petroleum products may occur. The coincidence of the following three conditions on the surface of a Buna-S vulcanizate will amost certainly lead to a serious tear: 1. Cracking (weather cracks, cuts, gouges, snags). 2. Wetting with petroleum products, particularly the lighter variety. 3. Flexing, static or dynamic. The tear will probably continue through the object until the flexing stress is relieved or until a fabric insert is reached. Thus, a tire tread would be torn through to the breaker fabric.

Buna S vulcanizates have been found to suffer serious losses in tear resistance when exposed to the influence of petroleum products, particularly the lighter variety. The conventional tests for swelling and loss of tensile strength in petroleum products are misleading when applied to Buna S vulcanizates because they give no indication of this failing. LITTLEinformation has been published concerning the solvent or oil resistance of Buna S. Street and Ebert (o) compared the swelling of stocks prepared from Hevea rubber, Buna S, Buna N, neoprene, and Thiokol in gasoline, benzene, two lubricating oils, and water. They found that the Buna S stock swelled approximately 60 per cent as much as the Hevea rubber stock in the gasoline and the two oils. Both Buna S and Hevea stocks swelled much more than the Buna N, neoprene, or Thiokol stocks in these solvents.The lack of interest in the oil and solvent resistance of Buna S is due to the fact that it is not intended for use where liquid hydrocarbons will come into contact with it. Nevertheless, in certain applications Buna S may have casual contact with gasoline or oils-for example, in tire treads, conveyor and