Effect of a small amount of sulfur on the physical and mechanical properties of peroxide‐cured fully saturated HNBR compounds

Abstract

Sulfur can be used as crosslink coagent in unsaturated elastomer. In this work, a fully saturated HNBR with 39 wt % nitrile content was selected to investigate the effect of a small amount of sulfur acting as crosslink coagent on the physical and mechanical properties of peroxide-cured vulcanizates. First, selective cleavage of polysulfide (ASxA) and monosulfide(ASA) bond by combined thiol-piperidine treatment were performed and the existence of poly/monosulfide bond in sulfur-contained HNBR compounds was verified. Then, no-filler HNBR compounds with various content of sulfur were investigated to detect the influence of sulfur on the crosslink density and cure kinetics. The MDR results showed that the crosslink density of HNBR compounds reduced only when the amount of sulfur is 0.25 phr and above. Besides, the curing rate of no-filler HNBR compounds increased with the increasing of the amount of sulfur and reached a maximum at a dosage of 0.25 phr sulfur. Finally, physical and mechanical properties of fully formulated compounds were evaluated and it was found that the addition of small amounts of sulfur in fully saturated HNBR compounds could improve the dynamic properties of peroxide-cured HNBR compounds remarkably but at a cost of slightly higher compression set values and a small loss in heat aging resistance. In a conclusion, small amount of sulfur can impart the peroxide vulcanizates some "sulfide properties" like dynamic property, tensile strength, but at the same time, due to the introduction of sulfur, some "peroxide vulcanizates property" like heat-resistance property, hot air resistance were weakened slightly.

A Novel Approach to Investigating Effect of Sulfur as a Coagent on the Quasi‐Static and Cyclic–Dynamic Fatigue Properties of Peroxide Cured EPDM

“…However, few work has been done to study the effect of sulfur or sulfur donors as coagent on network structure and on the cyclic–dynamic fatigue properties of peroxide cured rubbers. Sheng studied the effect of sulfur as the coagent on the properties of peroxide cured hydrogenated NBR and the results showed that small amount of sulfur could impart the peroxide vulcanizates some “sulfide properties” like dynamic property, tensile strength.…”

Relationship between the cross-link structure and properties of peroxide and sulfur-cured magnetic composites based on NR and NBR

“…However, there are also some disadvantages compared to sulfurcured systems, as low scorch safety and worse dynamic and elastic properties of vulcanizates. 7,8 As the cross-linking efficiency of peroxides is sometimes rather low, the so-called coagents are often introduced to boost peroxide vulcanization. 9,10 Coagents are mostly polar vinyl monomers with high affinity toward free radicals and readily graft to macromolecular chains to form a complex cross-linked network.…”

Effect of curing systems on vulcanization, mechanical properties, and stress softening of hydrogenated nitrile butadiene rubber vulcanizates

“…Generally, the cross-link bonds in HNBR vulcanizates cured by S are mainly polysulfide (C-S x -C, x > 2) bonds, and C-S-C bonds are formed in the S donor system, while C-C bonds occur in the peroxide system. 25 Different cross-link structure and cross-link bonds formed in the HNBR vulcanizates are shown in Figure 1. Among three kinds of the cross-link bonds, the sequence of the bond energy is as follows: C-C (peroxide) > C-S-C (S donor) > C-S x -C (S).…”