Crosslinking of Carboxylated Nitrile Rubbers with Resol Resins

Abstract

This paper discusses at length the metal oxide and sulfurfree crosslinking of rubber compounds for carboxylated nitrile rubber (XNBR) using resols based on p-alkyl phenols (resol crosslinking). It demonstrates that, with the best grade and dosage of resol and the right Krynac X nitrile rubber grade, such a compound can be adjusted to match the overall property profile resulting from traditional crosslinking with zinc oxide/sulfur with even better processing characteristics. Significant improvements can be achieved, for instance in the compression set characteristics. Resol crosslinking is sensitive to the grade of rubber used. The best and most balanced property profile can be achieved with XNBR grades containing 1% carboxylic acid (Krynac X 146, Krynac X 160). When the principles explained are observed, vulcanisates based on XNBR grades containing 7% carboxylic acid (Krynac X 750) also offer advantages. In addition to vulcanisates containing carbon black, compounds containing silica are also discussed and it is shown that, in this case, the additional use of silanes is indispensable for effective vulcanisation.