Preparation and characterization of nitrile butadiene rubber-nanoclay composites with maleic acid anhydride as compatibilizer. Part II: Physico-mechanical properties and thermo-oxidative aging

The influence of maleic acid anhydride-treated organoclay (MOC) content (i.e. 1, 3, 5, 10, 20 phr) relative to the micrometer clay (i.e. 10, 20 phr) on the nitrile butadiene rubber (NBR) compounds was analyzed through physico-mechanical properties (i.e. tensile strength, elongation at break, Young's modulus, hardness Shore A and crosslink density). The effect of (MOC) content on aging resistance of NBR nanocomposites at 90 +/- 1 degrees C for different time intervals (namely 2, 4, 6, 7 days) was also investigated through changes in aging properties, compared to unmodified micrometer clay composites (10, 20 phr) and unfilled NBR. The constants of the relative change in the physico-mechanical properties of NBR vulcanizate compounds were calculated. Physico-mechanical properties demonstrated an increase in the crosslink density for the MOC (3 phr)-incorporated NBR compound compared to conventional composites and pure NBR. Thermal aging data of the aged samples revealed that under aerobic hot aging conditions, NBR compounds undergo crosslink reactions that lead to embrittlement and ultimately failure. Incorporation of MOC filler, however, resulted in significant improvement of the degradation profile of the nanocomposites at 90 +/- 1 degrees C. Loss of tensile strength and flexibility during aging of the NBR nanocomposites with 3 phr MOC was milder, relative to unfilled polymer, indicating a restricted degradation by the MOC-filled rubber, thus prolonging the modulus. However, beyond 3 phr MOC, a deterioration in the aging properties of the nanocomposites takes place.