In this study, hydrogenated acrylonitrile butadiene rubber (HNBR, ZETPOL-2010L) and nitrile butadiene rubber (NBR, NIPOL-DN4555) were blended at different ratios in a Haake melt blender at 130°C. The HNBR and the NBR were of very similar acrylonitrile content and Mooney viscosity. The melt miscibility and solid-state properties were investigated by rheological, thermal, and mechanical testing and scanning electron microscopy (SEM) techniques. The dynamic viscosity of the blends followed the log-additivity rule, while the flow activation energy closely followed the inverse additivity rule. On the other hand, the storage modulus showed synergistic effects at all compositions, suggesting the presence of emulsion morphology at both ends of the composition range. For the 50/50 HNBR/NBR blend, the SEM micrographs suggest a uniform elongated structure. The thermal analysis showed the presence of two glass transitions, representing the pure components, at all blend ratios, suggesting the absence of segmental miscibility of the blends. The small-strain mechanical properties such as tensile modulus and yield stress followed linear additivity. However, HNBR and HNBR-rich blends were observed to strain harden at a rate higher than that of NBR. Induced crystallization of HNBR was suggested to be the reason for the strain hardening. The different rheological, thermal, and mechanical testing techniques agree in suggesting that the structurally similar HNBR and NBR are not thermodynamically miscible but mechanically compatible.

ABSTRACT:The thermomechanical modification of hydrogenated nitrile butadiene rubbers (HNBR) of different molecular parameters was investigated by rheological and light scattering techniques. The influences of acrylonitrile content, degrees of hydrogenation, and Mooney viscosity were examined. A melt blender with Banbury-type mixing blades was used to condition the rubber samples in the temperature range from 190 to 260°C. Light scattering was used to determine the effect of conditioning on MW and hydrodynamic radius of the rubber molecules. Dynamic viscosity (Ј) and storage modulus (GЈ) were measured for the as-received and conditioned samples. Experimental results showed that degradation in these rubbers occurred through chain scission and crosslinking. Depending on the molecular parameter, it was found that one of these two mechanisms dominated the degradation process in most brands. Addition of adequate amounts of antioxidants (Irganox 1010 and Irgafos 168) was successful only in preventing degradation by crosslinking. Compared to thermal degradation, thermomechanical degradation was found to be much more severe and progressed at much higher rates. Rheology was found to be a very sensitive technique to structural parameters of the polymers and could be used to detect and identify the mechanism of degradation.