Advances in Rubber Compounds Using ZnO and MgO as Co-Cure Activators

Abstract

Zinc oxide performs as the best cure activator in sulfur-based vulcanization of rubber, but it is regarded as a highly toxic material for aquatic organisms. Hence, the toxic cure activator should be replaced by a non-toxic one. Still, there is no suitable alternative industrially. However, binary activators combining ZnO and another metal oxide such as MgO can largely reduce the level of ZnO with some improved benefits in the vulcanization of rubber as investigated in this research. Curing, mechanical, and thermal characteristics were investigated to find out the suitability of MgO in the vulcanization of rubber. Curing studies reveal that significant reductions in the optimum curing times are found by using MgO as a co-cure activator. Especially, the rate of vulcanization with conventional 5 phr (per hundred grams) ZnO can be enhanced by more than double, going from 0.3 Nm/min to 0.85 Nm/min by the use of a 3:2 ratio of MgO to ZnO cure activator system that should have high industrial importance. Mechanical and thermal properties investigations suggest that MgO as a co-cure activator used at 60% can provide 7.5% higher M100 (modulus at 100% strain) (0.58 MPa from 0.54 MPa), 20% higher tensile strength (23.7 MPa from 19.5 MPa), 15% higher elongation at break (1455% from 1270%), 68% higher fracture toughness (126 MJ/m3 from 75 MJ/m3), and comparable thermal stability than conventionally using 100 % ZnO. Especially, MgO as a co-cure activator could be very useful for improving the fracture toughness in rubber compounds compared to ZnO as a single-site curing activator. The significant improvements in the curing and mechanical properties suggest that MgO and ZnO undergo chemical interactions during vulcanization. Such rubber compounds can be useful in advanced tough and stretchable applications.

Effect of Composition on Adhesion and Chemical Resistance in Multilayer Elastomer Laminates

“…A metal oxide (such as MgO) is necessary in BIIR and FKM vulcanization: it mainly acts as a retarder to prevent a fast cure of BIIR, while it functions as an acid scavenger absorbing hydrogen fluoride and fluoride byproducts during the cure and post curing of FKM . Alam et al found that MgO/ZnO binary and ZnO-only activator systems (along with SA) provided similar swelling index (in toluene) and cross-link density values for natural rubber, indicating a negligible effect of MgO/ZnO on chemical resistance. Ismail et al observed that the swelling index of natural rubber (in toluene) decreased slightly when increasing the loading of SA from 1 to 7 phr .…”

Critical Condition of Nanostructured Magnesium Oxide for Accelerated Sulfur Vulcanization of Natural Rubber

“…Magnesium oxide (MgO) attracts much attention as a vulcanization activator, instead of zinc oxide (ZnO), − which plays an important role in the accelerated sulfur vulcanization of natural rubber. This is because MgO has the potential to form a vulcanization intermediate when it reacts with a vulcanization accelerator.…”

Magnesium oxide synthesized with Alpinia zerumbet leaf extracts as a sustainable alternative to zinc oxide in nitrile rubber compounds: A comparative vulcanization kinetics investigation

“…Among the potential alternatives, magnesium oxide (MgO) appears to be an attractive candidate. [16][17][18][19][20] Roy et al, 19 compared nanosized MgO (0.5, 1, and 2 phr) and conventional ZnO (5 phr) in the vulcanization of unfilled NR compounds. According to the authors, the CRI of the NR compound containing 1 phr of nanosized MgO increased by 400% when compared to the compound with 5 phr of ZnO.…”

“…Nevertheless, it is important to consider that Roy et al, 19 employed a different vulcanization system (zinc(N-benzyl piperazino) dithiocarbamate: 1.7 phr, 2-mercapto benzothiazyl disulfide: 1.992 phr, and sulfur: 0.5 phr) than that used by Guzm an et al, (N-cyclohexylamine-2-benzothiazolesulfenamide: 1.2 and sulfur: 2 phr). 17,18 In a recent study, Alam et al, 16 stated that the use of MgO as a co-activator is an efficient way to reduce the ZnO amount in NR formulation. According to the authors, the MgO/ZnO-based binary activator system improves both vulcanization kinetics and mechanical properties as compared to the use of MgO alone.…”

“…The replacement of ZnO by other metal oxides is also a subject of interest. Among the potential alternatives, magnesium oxide (MgO) appears to be an attractive candidate 16–20 . Roy et al, 19 compared nanosized MgO (0.5, 1, and 2 phr) and conventional ZnO (5 phr) in the vulcanization of unfilled NR compounds.…”