Ionic Crosslinking of Carboxylated SBR
Abstract 1. Ionic bonding of carboxylated SBR with zinc oxide is detectable by means of measurements of the temperature dependence of tan δ. There is an α peak in the region of 60°C at 3.5 Hz. The position and shape of the α peak are strongly dependent on the state of cure of the vulcanizates. Without permanent crosslinking, the α peak is a plateau; as the crosslink density increases, the α peak becomes sharper and shifts to lower temperatures. The presence of carbon black causes the α peak to shift to higher temperatures, regardless of the presence of permanent crosslinks. 2. Ionic bonds in carboxylated SBR reacted with zinc oxide are in the form of ion clusters which function as crosslinks at room temperature. The ionic crosslinks provide carboxylated SBR with high tensile strength in the absence of reinforcing fillers. The presence of carbon black causes the 300% modulus to increase. The ionic crosslinks are labile, and the strength is lost at moderately elevated temperatures. A mixed cure system consisting of both sulfur and zinc oxide provides higher heat resistance than either of the single cure systems.