Structure development during dynamic vulcanization of hydrogenated nitrile rubber/nylon blends

The factors that influence the morphology and the interfacial parameters during dynamic vulcanization of hydrogenated nitrile rubber/nylon blends are examined. The particle size of the dispersed phase ( R̄ ) and the correlation distance (ξ) of a 50 : 50 blend decreased with increasing mixing time at 250°C, attained a minimum value, and then increased. The increase in the number of particles with time ( dn/dt ) may be expressed as ( dn/dt ) = k'n m , where n is the number of dispersed particles at time t , and m and k' are constants. R̄ and ξ gradually increased as the mixing temperature was increased from 250 to 300°C at a constant mixing time of 10 min. The particle size increased also with the increasing gel fraction of the rubber. At a constant mixing time of 10 min at 250°C, the particles were larger when the addition of the cross‐linker was delayed. These observations can be explained with the help of a hypothetical model, similar to that proposed by Wu, considering the breaking down of rubber particles, coagulation and coalescence of droplets, and droplet rupture in a matrix of nylon. On vulcanization, the thickness of the interface (λ) reduced from 62 to 48 nm. The interaction parameter and interfacial tension, as estimated from λ, for a bilayer specimen vulcanized in situ , at 250°C were 2.8 × 10 –3 and 0.24 mN/m, respectively. The high value of λ for the dissimilar polymer pair may be due to polymer‐polymer graft formation at high temperature. © 1993 John Wiley & Sons, Inc.