Crosslink Distribution and Interfacial Adhesion in Vulcanized Blends of NR and NBR

Abstract

Abstract In contrast to expectations from rheometer studies of vulcanization behavior, the NMR technique has demonstrated that blends of NR and NBR vulcanized with sulfur/TMTM show a marked distribution of crosslinks in favor of the NR phase. The presence of even a minor proportion of NBR is sufficient to reduce the degree of vulcanization of the NR phase below levels deemed to be technologically necessary. Replacing the sulfur with a bis-alkylphenol disulfide reduces the degree of preferential distribution of crosslinks substantially. Interpretation of differential-swelling data for the blends on the basis of the swelling expected from a single polymer vulcanized with the same level of curatives as added to the blend gives the impression that the blends are lacking in interfacial adhesion. The interpretation enabled by the NMR estimates of degrees of crosslinking for the phases within the blends demonstrates that there is no lack of interfacial adhesion in blends of NR and NBR having a low acrylonitrile content, although blends containing a minor proportion of NR and vulcanized with sulfur/TMTM may show cohesive failure of the NR phase when the NBR phase is highly swollen due to the low degree of crosslinking of the NR.