Accelerated Heat Aging Test for NBR with Renewable Antioxidant

Vulcanized nitrile rubber (NBR) compounds are subjected to degradation at elevated temperatures as well as oxidation due to the unsaturation in the polymer chains. A variety of antioxidants (AO) are used in NBR compounds to improve their heat and oxidation resistance. Standard tests of deterioration of vulcanized NBR in the hot air can be found in ASTM’s D 573 and D 2000 that require extensive sample preparation and long hours of aging in a convection oven. A reliable screening test with easy sample preparation and shorter testing time would be a great relief for the compound development.

Thermo gravimetric analysis (TGA) is a powerful tool to study polymer degradation. A testing protocol is developed in this study to run TGA on NBR compounds with different antioxidants. Results of TGA will be analyzed and compared with ASTM D 573 in this study.

One of the antioxidants used in this study is cashew nut shell liquid (CNSL) resin. The advantage of using CNSL resin as the AO is the possible co-vulcanization with nitrile rubber because of the presence of carbon-carbon double bonds in CNSL. This will result in a permanent bonding between the AO and NBR to achieve better heat aging properties such elongation and cold temperature flexibility. The rigidity of polymer chain can be monitored by its glass transition temperature. Differential scanning calorimetry (DSC) will be used in this study to measure the changes of Tg of NBR after heat aging and the results will be correlated to both TGA and ASTM D 573.