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)