Effect of high-temperature curing on the crosslink structures and dynamic mechanical properties of gum and N330-filled natural rubber vulcanizates

The effects of high-temperature curing and overcuring on the cure character istics, crosslink structure, physical properties and dynamic mechanical pro perties (DMPS) of gum and carbon black (N330) filled natural rubber (NR) vu lcanizates cured with conventional (CV), semi-efficient (SEV) and efficient (EV) cure systems, which have about the same total crosslink densities und er a moderate curing temperature of 150 degreesC, were investigated. The gu m NR vulcanizates cured with CV, SEV and EV curing systems have about the s ame glass transition temperature (T-g) and tan delta values below the tempe rature of about 0 degreesC, but showed some apparent differences in the tan delta values increasing in the order CV < EV in the relatively high temper ature region from 0 degreesC to 80 degreesC. The presence of N330 carbon bl ack in NR vulcanizates makes their elastic modulus G ' and tan delta values above T-g higher than those of the gum NR vulcanizates. High-temperature curing and overcuring cause decreases to various extents i n the cure plateau torque, Shore A hardness, 300% modulus and tensile stren gth, and lead to apparent changes in the DMPs. Typically, there is an incre ase in T-g of all three kinds of gum and N330-filled NR vulcanizates becaus e of changes in the total crosslink densities and crosslink types. The CV v ulcanizates show the most significant change in cure characteristics, physi cal properties and DMPs since the highest content of polysulfidic crosslink s appears in the CV vulcanizate, causing the highest level of reversion and having a dominant effect on the properties. (C) 2001 Elsevier Science Ltd. All rights reserved.