Dynamic mechanical properties in natural rubber/styrene-butadiene rubber blends: The local strain behavior in the glass transition region

Abstract

A study of the local strains developed in vulcanized blends of natural rubber (NR) and styrene butadiene rubber (SBR), prepared by solution mixing, is presented. A semi-EV system based on sulfur and accelerator was used for curing unfilled compounds at 160°C and 170°C. Samples were characterized by dynamic mechanical properties between −80°C and 20°C. Special interest was placed on the glass transition region of the vulcanized immiscible blends, where the NR and SBR phases are rubbery and glassy respectively. From the study of loss modulus, this research demonstrates how the local strain in the NR phase changes as a function of the amount of SBR in the blend. Assuming a coalescence behavior of the SBR glassy phase above a certain concentration, differences in the local stiffness of each phase in the glass transition regime were found. While in the glassy SBR phase the stiffness slightly varies with the NR/SBR content, a notorious increase was obtained in the rubbery NR phase at higher SBR content. The local strain on the NR phase of the blends shows a slight decrease for the samples vulcanized at 170°C compared with those vulcanized at 160°C.