Low-Temperature Properties of Hydrogenated Nitrile Rubber (HNBR)

Abstract

Abstract HNBR, hydrogenated nitrile rubber, is a heat-, oil-, and fuel-resistant elastomer produced by the selective hydrogenation of NBR. As shown in Table I, HNBR is a highly saturated nitrile elastomer consisting of units of acrylonitrile, ethylene, unsaturated butadiene, and hydrogenated vinyl butadiene. The acrylonitrile gives excellent oil resistance, fuel resistance, and high tensile strength to NBR. The ethylene provides not only excellent rubber elasticity, heat resistance, chemical resistance, and ozone resistance, but also good low-temperature flexibility. The presence of a small unsaturated portion in the butadiene unit makes possible the easy vulcanization of HNBR with either sulfur or peroxide. The vinyl butadiene segments (6–8%) are preferentially hydrogenated at the beginning of the reaction and assist in maintaining the amorphous nature of the elastomer. The low-temperature flexibility of ordinary NBR varies in inverse proportion to its acrylonitrile content. Therefore, low-acrylonitrile NBR has better low-temperature flexibility than high-acrylonitrile NBR. The low-temperature properties of HNBR are different than those of NBR. This paper will show the relation between the acrylonitrile content and degree of hydrogenation and the glass-transition temperature (Tg) and low-temperature flexibility of HNBR. The Tg and low-temperature flexibility as measured by the TR-test and Gehman Torsional Stiffness test of HNBR showed the different behaviors for the various degrees of hydrogenation and acrylonitrile contents. Conversely, the brittle temperature of HNBR becomes lower with an increase in degree of hydrogenation. This paper also describes the effects of polymer composition and of various plasticizers on the low-temperature flexibility of HNBR.