Vulcanization kinetics of acrylonitrile‐butadiene rubber reinforced with graphene oxide and reduced graphene oxide in the absence of co‐cure accelerator

Abstract

The market demand for elastomeric‐graphene/derivatives nanosheets (GDS) materials is high nowadays, due to their excellent physico‐mechanical properties over traditional composites. However, the curing behavior of elastomeric‐GDS which influences the overall properties and also determines the cost of related products has not been well investigated. Previously, the curing properties of NBR‐graphene oxide (GO) and NBR‐reduced graphene oxide (rGO) was studied and the curatives (accelerator and activators) were suspected to have influence on their curing behavior. This study explores the curing behavior of NBR‐GO and NBR‐rGO in the absence of tetramethylthiuram disulfide (TMTD) accelerator. The virgin NBR exhibited shorter curing periods with higher curing rates (CRI) than the composites. The measured CRI showed close correlation with the activation energy Ea, deduced from Ozawa and Kissinger kinetics models. The NBR‐rGO composites showed shorter scorch time and lowered Ea at higher temperatures, with increased tensile properties than NB‐GO composites. Despite the delay, the composites exhibited high strength over the virgin NBR, due to tighter networks introduced by rGO and GO sheets within NBR. Therefore, future design of elastomer‐GDS‐based composites must involve a careful control of the amounts of the accelerator‐/co‐accelerator‐like TMTD in the mixtures for improved physico‐mechanical properties of the final product.

Investigating the Effect of Curing Activators on the Cure Kinetics of Acrylonitrile–Butadiene Rubber Filled with Graphene Oxide and Reduced Graphene Oxides Nanocomposites

“…The pH of the synthesized GO nanosheets was ~5.0, whereas that of the rGO nanosheets range from ~6 to 8 upon the intensive reduction by using NH 4 OH and hydrazine solutions. The GO and rGO used in this work had a thickness within ∼0.83-2 nm and hydrodynamic size within 100-120 nm [32]. Table 1 shows the compound design expressed as phr.…”

“…The ZnO forms zinc stearate, which activates the action of the accelerator system to increase the efficiency of vulcanization [23][24][25][26]. In the end, infinite crosslinks/network structures are formed as a result of the reactions among the sulfurating species and with the saturated (-C=C-) sites of the rubber matrix [9,10,32].…”

“…Rubber-GDS composites vulcanization have generated an ongoing debate, as to whether GDS delays or shortens the time for vulcanizing a virgin rubber matrix. The delay is a measure of higher values recorded for the on-set of curing time (t s1 , t s2 , or t s5 ) and the optimum curing time (t 90 and t 95 ) [1,8,[32][33][34] deduced from rheo-curves [1,9,10,33,35,36]. The changes in curing times with respect to the torque can further be computed into activation energies (kJ/mol) by using popular kinetic models like that of Kissinger [37] and Ozawa [38].…”

“…Mensah et al [44,45] further observed that differences in functional group (-C-O-C-), carboxyl (-O-C=O), and hydroxyl (-OH), on GDS (GO and rGO) and the difference in the chemistry of the cure ingredients (curing agent, accelerator, and activator), may greatly influence the overall curing of rubber-GDS composites. To verify whether the absence of accelerators or activators would delay or increase cure reactions, in relation to physico-mechanical properties of the compounds, Mensah et al [32], initially prepared NBR-GO compounds with sulfur accelerating components without tetramethylthiuram disulfide (TMTD), and the results confirmed that curing was strongly dependent on the oxygen-carbon ratio of GDS.…”

“…Vulcanization tests were done using cure rheometer and differential scanning calorimetry (DSC) techniques. The cure and other properties of NBR-GO/rGO without ZnO/SA were compared with representative samples of NBR-graphite (GRT), those containing all the curing ingredients [44,45] and those prepared without TMTD [32]. The findings provide insights on controlling the curing speed of rubber-GDS composites with the cure ingredients, without compromising their mechanical integrity for future applications.…”