The dumbbell-shaped specimens of vulcanizates (thickness,
1 mm) were placed in an aging oven (GT-7017, Gotech Testing
Machine Inc., Taiwan) at 100 C for accelerated aging. With a certain
time interval, the samples (4 pieces per sample) were taken out
from the aging oven. The changes of the tensile strength (sbreak) and elongation at break ( 3break) of the samples due to thermal
oxidative aging were monitored by using a tensile strength tester
(UT-2080, U-CAN Dynatex Inc., Taiwan) at a crosshead speed of
500 mm min1. The aging coefficient (k) was used to evaluate the
antioxidative ability of the antioxidant for NR and calculated using
Equations (1) and (2).