Crosslinking of carboxylated nitrile rubber (XNBR) induced by coordination with anhydrous copper sulfate

Abstract

AbstractBACKGROUND: Crosslinking induced by non‐covalent interactions in rubber materials is currently attracting a great deal of interest because of its perceived reversibility. Some thermoplastic elastomers and ionic elastomers, which are crosslinked by physical entanglements and ionic bonds, respectively, have already been investigated. The present work is centred on the study of the influence of coordination bonds on the physical properties of crosslinked materials. These bonds are formed on addition of copper sulfate.RESULTS: In this context, the effect of crosslinking of carboxylated nitrile rubber (XNBR) by anhydrous copper sulfate (CuSO4) on crosslink reaction and mechanical and mechano‐dynamic properties is studied. The influence of different levels of CuSO4 and the addition of conventional filler, carbon black, on the network is studied. The presence of nitrile (CN) in the elastomeric chains leads to the formation of coordination bonds with the nitrile groups. The formation of ionic bonds between copper ions and carboxylic groups can be deduced from X‐ray photoelectron, attenuated total reflectance Fourier transform infrared and NMR analyses and vulcanization measurements. The dynamic response of the material does not show a secondary transition, the so‐called ionic transition typical of ionic elastomers, since ionic bonds do not lead to a separated ionic microphase, immersed in the elastomeric matrix.CONCLUSION: As expected, the crosslink density of the polymer network increases with the amount of crosslinking agent. Because of the presence of polymer–filler interactions, an increase in crosslink density is observed. However, these interactions seem not to affect the formation of coordination or ionic bonds. Copyright © 2008 Society of Chemical Industry