Conventional, semi-EV and EV sulfur systems

Crosslink length

Sulfur builds bridges of different lengths between rubber chains: one sulfur atom (monosulfide), two sulfur atoms (disulfide) or many sulfur atoms (polysulfide).

Polysulfide bonds are flexible; fatigue and tear resistance are high but they break with heat. Mono/disulfide bonds resist heat and ageing but dynamic performance is slightly lower.

What sets the ratio: sulfur / accelerator

When sulfur is high and accelerator is low, polysulfide bonds increase (conventional system). When sulfur is low and accelerator or sulfur donor is high, short bonds increase (EV: efficient vulcanization).

Semi-EV lies between the two and is the balance point in many technical parts.

Sulfur donors

In EV systems, part or all of the elemental sulfur is replaced with sulfur donors: TMTD, DTDM, CLD, DPTT. These materials deliver sulfur in active form during the reaction and support short bonds.

Reversion

In conventional systems, with long cure times or high cure temperatures, polysulfide bonds break and properties fall back; this is called reversion. It is pronounced in thick tire sections.

Measures: move to a semi-EV/EV system, use sulfur donors, or add an anti-reversion agent (PDM, TBSI).

How to choose?

Parts carrying dynamic loads (tires, belts, vibration mounts) need a conventional or semi-EV system. Static parts working in hot environments (seals, hoses) need semi-EV or EV.

The ranges in the table are general literature values; the exact ratio is determined in the compound formulation by rheometer and ageing tests.