Facilitating high-temperature curing of natural rubber with a conventional accelerated-sulphur system using a synergistic combination of bismaleimides

Abstract

It is well known that high-temperature curing of natural rubber (NR) with a conventional accelerated-sulfur (CV) system is limited because of reversion. This paper describes the curing behavior and the reversion resistance characteristics of unfilled NR with a CV system in the presence of two different bismaleimides: Perkalink 900 (PL) and Maleide F (MF). Rheometer studies reveal that MF can directly interact with the NR during accelerated-sulfur curing and forms some thermally stable bismaleimide type crosslinks in the beginning via Alder-ene reaction. However, even with the use of 4 phr of MF, a considerable reversion was noticed during the curing of NR with CV at 180 °C for 1 hr. A high dosage (5 phr) of MF was therefore required for a complete reversion free plateau type cure pattern. On the other hand, PL has no direct interaction with the NR at the beginning of the curing reaction. Moreover, even 1 phr PL exhibits a marching modulus curing behavior via Diels-Alder reaction. Therefore, to solve the individual issues of these chemicals, a synergistic combination of MF and PL has been identified and applied to facilitate the high-temperature curing of NR/CV devoid of reversion with a plateau type cure pattern.

Keywords

• rubber
• curing
• reversion
• bismaleimide
• diels-alder reaction