Effect of Sulfur during Radiation Curing of Poly(Vinyl Ethyl Ether) and Ethylene-Propylene Rubber

Abstract

Abstract A study was made of the effect of sulfur, during radiation curing, on the physical properties of poly(vinyl ethyl ether) and an ethylene/propylene copolymer containing HAF carbon black. The presence of sulfur enabled the attainment of higher maximum tensile strength and generally higher crosslink density than when sulfur was omitted. Furthermore, the maximum tensile strength of the sulfur-containing samples was obtained at a lower radiation dose than in the corresponding control experiments. For a given swelling ratio, a higher tensile strength was generally obtained for samples irradiated in the presence of sulfur. For a given dose of radiation, the per cent elongation-at-break values of poly(vinyl ethyl ether) samples decreased as the amount of sulfur in the recipe was increased. In contrast, in the ethylene/propylene rubber the presence of sulfur resulted in an increase in the elongation values. The per cent sol values were also quite high for the ethylene/propylene vulcanizates as compared to the corresponding values in poly(vinyl ethyl ether) samples. In both rubbers, lower sol values were obtained in the presence of sulfur. Chemically bound sulfur was found in poly(vinyl ethyl ether) samples irradiated in the presence of elemental sulfur or dicyclopentamethylene thiuram tetrasulfide. The ability of the network to lose a portion of the combined sulfur by reaction with triphenyl phosphine may indicate that some of the crosslinks contain disulfide and/or polysulfide groups.