Effect of crosslink structures on dynamic mechanical properties of natural rubber vulcanizates under different aging conditions

The effects of crosslink structures on the dynamic mechanical properties (DMPs) of unfilled and carbon black N330-filled natural rubber (NR) vulcanizates cured with conventional(CV), semiefficient (SEV), and efficient (EV) cure systems and having about the same total crosslink densities were investigated before and after aerobic and anaerobic aging at 100 degreesC. The three unfilled NR vulcanizates cured with the CV, SEV, and EV systems had about the same mechanical loss factor (tan delta) values at about 0 degreesC but showed some apparent differences in the tan delta values in the order EV > SEV > CV at relatively high temperatures of 40-80 degreesC before aging. However, N330-filled NR vulcanizates gave higher tan delta values than the unfilled vulcanizates and showed little effect of the crosslink types on the tan delta at different temperatures over the glass-transition temperature (T-g) before aging. Aerobic heat aging increased the T-g and tan delta values of the vulcanizates over a wide range of temperatures from -80 to 90 degreesC that was mainly due to the changes in the total density and types of crosslinks. The unfilled vulcanizates cured with the CV system showed the greatest change in DMP because of their poor resistance to heat aging. Aerobic heat aging of NR vulcanizates caused a more significant change in the DMP than anaerobic heat aging because of the dominant effect of the oxidative degradation during aerobic heat aging on the main-chain structure, crosslink structures, and DMPs of the vulcanizates. (C) 2001 John Wiley & Sons, Inc.