TMTD in EV and Semi-EV Vulcanisation Systems

Tetramethylthiuram disulfide (TMTD, CAS 137-26-8) earns its place in modern rubber compounds less as a fast accelerator and more as a sulfur donor – the reagent that supplies the crosslinking sulfur in low-sulfur and sulfurless (“efficient vulcanisation”, EV) systems. This article explains the EV idea, where TMTD fits, and what it gives the compound.

1. The vulcanisation basics

A sulfur vulcanisation system has three parts: the sulfur (or a sulfur donor), the accelerator (which controls how fast and how the crosslinks form), and the activators (typically zinc oxide with stearic acid). Changing the ratio of sulfur to accelerator changes the type of crosslink and therefore the properties of the rubber.

2. Conventional, semi-EV and EV

System	Sulfur	Accelerator / donor	Crosslink type	Result
Conventional	High (about 2 – 3 phr)	Low accelerator	Mostly polysulfidic	Good fatigue and tear, lower heat resistance
Semi-EV	Medium (about 1 – 1.7 phr)	Higher accelerator	Mixed	Balance of fatigue and heat ageing
EV (efficient)	Low or none (about 0 – 0.5 phr)	High accelerator + sulfur donor	Mostly mono- and disulfidic	Better heat resistance, lower compression set, better ageing

As sulfur is reduced, the crosslinks become shorter and more thermally stable – which is why EV compounds resist heat ageing and hold their shape better. The catch is that the sulfur still has to come from somewhere: that is the job of the sulfur donor.

3. TMTD as a sulfur donor

TMTD is a disulfide: two dimethylthiocarbamoyl groups joined through an S-S bond. In the cure it can donate sulfur to form crosslinks and also acts as an ultra-accelerator. That dual role makes it one of the main sulfur donors for EV systems.

Sulfur donor	Note
TMTD	Thiuram disulfide; accelerator + donor
TETD	Thiuram disulfide; similar role
DTDM (morpholine disulfide)	Sulfur donor without accelerating action

TMTM (the monosulfide) is an accelerator but not a sulfur donor, which is a common point of confusion.

4. What TMTD gives the compound

Property	Effect of using TMTD in an EV system
Heat ageing	Improved (more thermally stable crosslinks)
Compression set	Lower – better sealing and dimensional stability
Reversion	Reduced at high cure temperatures
Fatigue / flex	Lower than a high-sulfur system – a trade-off to balance
Cure speed	Very fast (thiuram), often needs a scorch-safe co-accelerator

5. Typical dosage

Role	Typical dosage (starting point)
Sulfur donor in EV	About 1.0 – 3.0 phr
Secondary accelerator	About 0.2 – 1.0 phr
Latex / low-temperature cure	Set by the system

Because TMTD cures so fast, the sulfur-to-accelerator balance and any co-accelerator (thiazole or sulfenamide) must be set to keep enough scorch safety for processing. Confirm the whole system by cure rheometry.

6. Where EV compounds are used

Engine mounts and vibration isolators – low set and heat resistance.
Hoses and seals – where hot service and permanent set matter.
Belts and technical goods – heat-ageing resistance over long service.
Compounds cured at high temperature – EV systems resist reversion better than conventional ones.

7. Handling and regulation

Skin and respiratory sensitizer – use dust control, ventilation and suitable gloves.
Harmful if swallowed / in contact with skin; eye irritant; very toxic to aquatic life.
Alcohol reaction – TMTD can cause a disulfiram-like reaction with alcohol; warn workers.
Regulatory – as an industrial rubber chemical TMTD is widely used; as a plant-protection product (thiram) it is restricted in some regions. Confirm the requirements for your market.

Frequently Asked Questions

What is an EV vulcanisation system?

A low-sulfur or sulfurless system that uses a high accelerator level plus a sulfur donor. It gives more thermally stable crosslinks, so better heat ageing and lower compression set.

Why is TMTD used in EV systems?

Because it is both an ultra-accelerator and a sulfur donor – it supplies the crosslinking sulfur when elemental sulfur is reduced or removed.

How much TMTD is used as a sulfur donor?

Typically about 1-3 phr in an EV system, set by the formulation and confirmed by cure rheometry.

Is TMTD a sulfur donor or just an accelerator?

Both. It is an ultra-accelerator and a sulfur donor; TMTM (the monosulfide) is an accelerator but not a donor.