Curing and mechanical behavior of carboxylated NBR containing hygrothermally decomposed polyurethane

Hygrothermally decomposed polyester-urethane (HD-PUR) has been added as modifier (up to 20 phr) to sulfur crosslinked carboxylated nitrile rubber (XNBR). The curing and mechanical characteristics of the XNBR have been investigated as a function of the HD-PUR loading in presence and absence of carbon black (CB). The addition of HD-PUR increased the cure rate of both unfilled and CB filled XNBR but resulted in compounds of lower crosslink density and thus of lower stiffness and strength. Based on infrared spectroscopic results it was speculated that the amine functionality of HD-PUR affected the formation of the ionic clusters formed by the reaction between the -COOH groups of XNBR and ZnO. This occurred likely via a coordination complex. Evidence was also found for the formation of -CONH- linkages. Both coordination complexing and chemical reaction between -COOH and -NH₂ resulted in a lower overall “crosslinking degree” and as a consequence HD-PUR acted as plasticizer in XNBR.