Characterization of NBR networks from stress–strain and swelling equilibrium measurements

Abstract

An improved stress–strain (S/S) method based on rubber elasticity theory and swelling equilibrium measurements was used to investigate the S/S behavior and the solvent swelling properties of nitrile–butadiene rubber (NBR) and also to study the effects of varying the cure agent and the curing conditions on the crosslinking efficiency in NBR vulcanizates. The S/S curve of completely swollen NBR vulcanizates is, as expected, in agreement with rubber elasticity theory, while that of dry or partially swollen vulcanizates is well described by the Mooney‐Rivlin equation. Determined in benzene, χ was 0.494, compared to 1.338 in cyclohexane and 2.124 in n‐heptane. The degree of crosslinking and the crosslinking efficiency in the NBR vulcanizates, moles of crosslinks produced per mole of crosslinking agent employed in the formula, are largely dependent on the nature of the crosslinking agent used and increase in the following order: peroxide, sulfur tetramethylthiuram disulfide, sulfur N‐cyclohexyl‐2‐benzothiazolesulfenamide, sulfur benzothiazyl disulfide, and finally tetramethylthiuram disulfide.