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 (RBAR) and the correlation distance (xi) of a 50 : 50 blend decreased with increasing mixing time at 250-degrees-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. RBAR and xi gradually increased as the mixing temperature was increased from 250 to 300-degrees-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-degrees-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 (lambda) reduced from 62 to 48 nm. The interaction parameter and interfacial tension, as estimated from lambda, for a bilayer specimen vulcanized in situ at 250-degrees-C were 2.8 X 10(-3) and 0.24 mN/m, respectively. The high value of lambda for the dissimilar polymer pair may be due to polymer-polymer graft formation at high temperature. (C) 1993 John Wiley & Sons, Inc.