Fundamental Considerations for the Covulcanization of Elastomer Blends. II. Lead Oxide-Activated Cures of NBR-EPDM Blends

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Abstract
We have determined the cause for the covulcanization behavior of NBR-EPDM blends in TETD accelerator-lead oxide activator formulations. The key lies in the fact that the lead salts of TETD are insoluble in both polar and nonpolar materials. This insolubility would remove the thermodynamic driving force for curative diffusion between elastomer phases and result in a uniform concentration of accelerator salt in both phases. The resulting blends would then be well vulcanized in both phases and exhibit good properties. These observations are consistent with the hypothesis that lack of covulcanization is due to the diffusion of the accelerator into the more polar and/or faster curing phase of an elastomer blend.