Effect of Crosslink Structures on Dynamic Mechanical Properties of Natural Rubber Vulcanizates under Different Aging Conditions

摘要

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 (CY),semiefficient (SEY), and efficient (EY) cure systems and having about the same total crosslink densities were investigated before and after aerobic and anaerobic aging at 100degC. The three unfilled NR vulcanizates cured with the CY, SEY, and EY systems had about the same mechanical loss factor (tan #delta#) values at about 0degC but showed some apparent differences in the tan #delta# values in the order EY > SEY > CY at relatively high temperatures of 40-80degC 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 temperaJ;ure (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 90degC that was mainly due to the changes in the total density and types of crosslinks. The unfilled vulcanizates cured with the CY 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.