Compounding rubber for radiation resistance

Compounding techniques to improve the radiation resistance of butadiene-styrene tread vulcanizates in a radiation field are described. These include extension of rubber with an aromatic oil, incomplete curing of stocks containing sulfur vulcanization agents, and incorporation of additives. Incomplete curing produces vulcanization intermediates, which are affected by the ratio of sulfur to accelerator and by cure temperature and which are resistant to radiation. A combination of all these factors improved the lifetime of cold-rubber tread vulcanizates by a factor of 5 to 6. Swelling and stress-relaxation techniques are applied to follow quantitatively changes in the polymeric network, which are used to explain changes in stress-strain properties. These techniques indicate that much of the scission that occurs is more than compensated for by crosslinking. Dilution of the polymer network with an aromatic oil decreases the ratio of crosslinking to scission to produce a more radiation-resistant material. In the absence of oil, the decrease in radiation damage obtained by incomplete curing and with antirads is primarily the retardation of the crosslinking reaction. However, in the presence of oil, incomplete curing promotes and antirads retard radiation-induced crosslinking and scission about equally. Substitution of air for helium as an irradiation atmosphere serves to accentuate the scission reaction and to lessen radiation-induced changes in physical properties. A number of previously unreported retarders of radiation damage (antirads) are described.