Multiphase polymer processing: Controlled‐ingredient‐distribution mixing and its effect on some properties of styrene‐butadiene (SBR)/butadiene‐acrylonitrile copolymer rubber blend compounds

Abstract

AbstractThe flex‐crack‐growth resistance and oil‐swelling resistance of a styrene‐butadiene (SBR)/butadiene‐acrylonitrile co‐polymer (NBR) rubber blend are studied as a function of the distribution of ingredients in the individual rubber phases. The blends consist of 70:30 weight ratio of SBR:NBR with incorporation of 82.5 phr carbon black and other ingredients via the controlled‐ingredient‐distribution mixing procedure. The results show that flex crack growth is affected by the distribution of carbon black. Better flex crack growth resistance could be achieved by adding 10 percent of carbon black to the NBR rubber phase and 90 percent to the SBR phase. The swelling of these rubber blends in ASTM #2 oil is also affected by the location of carbon black and by the mixing history. The blends with more black initially preloaded in the SBR phase have lower swelling, as have blends with shorter cross‐mixing time or the mill. A simple equation based on the permeation/moduli of composite materials is proposed to describe the swelling of this rubber blend in terms of the swelling of the constituent rubber phases, the distribution of ingredient in the individual rubber phases, and the blend morphology. One of the key assumptions is to consider the individual black preloaded rubber as a continuum. The quantitative correlation with the observed swelling data is reasonably good.