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

Abstract

The effects of high-temperature curing and overcuring on the cure characteristics, crosslink structure, physical properties and dynamic mechanical properties (DMPs) of gum and carbon black (N330) filled natural rubber (NR) vulcanizates cured with conventional (CV), semi-efficient (SEV) and efficient (EV) cure systems, which have about the same total crosslink densities under a moderate curing temperature of 150°C, were investigated. The gum NR vulcanizates cured with CV, SEV and EV curing systems have about the same glass transition temperature ( T g) and tan δ values below the temperature of about 0°C, but showed some apparent differences in the tan δ values increasing in the order CV<EV in the relatively high temperature region from 0°C to 80°C. The presence of N330 carbon black in NR vulcanizates makes their elastic modulus G′ and tan δ values above T g higher than those of the gum NR vulcanizates. High-temperature curing and overcuring cause decreases to various extents in the cure plateau torque, Shore A hardness, 300% modulus and tensile strength, and lead to apparent changes in the DMPs. Typically, there is an increase in T g of all three kinds of gum and N330-filled NR vulcanizates because of changes in the total crosslink densities and crosslink types. The CV vulcanizates show the most significant change in cure characteristics, physical properties and DMPs since the highest content of polysulfidic crosslinks appears in the CV vulcanizate, causing the highest level of reversion and having a dominant effect on the properties.