Influence of vulcanization temperature on the cure kinetics and on the microstructural properties in natural rubber/styrene-butadiene rubber blends prepared by solution mixing

Abstract

Blends of natural rubber and styrene-butadiene rubber were prepared by solution mixing and vulcanized with a system sulfur–accelerator at 433 K and 443 K in order to study the vulcanization kinetic and the influence of the vulcanization temperature on the final structure of the blends. The kinetic of vulcanization was analyzed under the frame of the Han’s model, which takes into account the reversion effect once the time to achieve the maximum torque in the rheometer curves is surpassed. The crosslink density was also determined in all samples by means of swelling in solvent. The average free nanohole volume was estimated using positron annihilation lifetime spectroscopy. When changing the vulcanization temperature of the blends, remarkable changes in the crosslink densities and the free nanohole volumes were detected. Furthermore, a correlation between the average fractional free nanohole volume and the fraction of polymer in the swollen state was established.