Accelerators

Accelerators play a key role in the vulcanisation process, in which natural rubber acquires its elastic properties through the addition of sulphur or peroxide and the action of heat. They promote the formation of sulphur bridges between the polymer chains, making the rubber compound more stable and resistant.

Vulcanisation process

In the vulcanisation process, sulphur or peroxide bonds with the double bonds of the rubber molecules and forms a three-dimensional network. Accelerators shorten the time needed for this reaction and increase the efficiency of the sulphur or peroxide bonding. Without accelerators, the vulcanisation process would take too long and lead to uneven results.

There are various types of accelerators, which are used depending on the type of elastomer and the desired product properties. The most common types include thiazole-based, sulfenamide-based and thiuram-based accelerators.

Thiazoles

Thiazole-based accelerators such as MBT (2-mercaptobenzothiazole) are particularly widespread in the elastomer industry. They offer moderate acceleration and are often used for applications that require a good balance between processability and vulcanisation speed.

• Advantages: good balance between vulcanisation speed and end product properties.

• Applications: used in tyre rubber compounds, conveyor belts, sheet material and moulded rubber parts.

Sulfenamides

Sulfenamide-based accelerators such as CBS (cyclohexylbenzothiazole sulfenamide) offer a slower onset followed by rapid vulcanisation. These properties make them ideal for thick-walled rubber products that require uniform vulcanisation over longer periods.

• Advantages: high efficiency for thick-walled, voluminous products, good thermal resistance.

• Applications: used in tyres, seals and various sealing elements.

Thiurams

Thiuram-based accelerators such as TMTD (tetramethylthiuram disulphide) are very fast-acting accelerators. They offer an extremely high vulcanisation speed and are often used as secondary accelerators to speed up the process when working in combination with other accelerators.

• Advantages: very fast vulcanisation speed, can be combined with other accelerators.

• Applications: used in extrudates, moulded rubber parts and profiles.

Accelerators offer numerous advantages in elastomer production, affecting production efficiency, cycle times and the quality of the end product:

• Faster vulcanisation: shortens the time needed for the vulcanisation process and so enables higher production speeds.

• Improved product properties: increases the mechanical stability, ageing resistance and elasticity of the respective elastomer.

• Energy savings: faster vulcanisation can reduce energy consumption in production, which leads to lower operating costs.

Vulcanisation accelerators are used in a wide range of applications in elastomer processing. They are crucial for the manufacture of products that are exposed to mechanical and dynamic loads.

Tyre manufacturing

In the tyre industry, vulcanisation accelerators play a central role, as they ensure uniform crosslinking and permanent elasticity of the elastomer. Accelerators such as CBS and MBT are standard components in tyre rubber compounds.

Technical elastomer products

Seals, moulded articles, hoses and sheet material are other important applications for vulcanisation accelerators in the production of the respective rubber compound. These products must be robust, elastic and resistant to a variety of conditions.

The following table compares the most common types of vulcanisation accelerators in terms of their properties and applications:

Accelerator type	Vulcanisation speed	Thermal resistance	Applications
Thiazoles (MBT)	Medium	Medium	Tyres, conveyor belts, technical products
Sulfenamides (CBS)	Slow at first, then fast	High	Tyres, thick-walled rubber products
Thiurams (TMTD)	Very fast	Low	Latex products, hoses, cables

1. Why are accelerators so important in elastomer processing?

Accelerators shorten the time needed for vulcanisation while improving the quality of the end product. Without them, the process would be too slow, too costly and inefficient.

2. Which factors determine the choice of the right accelerator?

The choice of the right accelerator depends on the type of elastomer, the production requirements and the specific applications. Factors such as vulcanisation speed, thermal resistance and product properties play a role.

3. Can accelerators be combined?

Yes, different accelerators are often combined to take advantage of the individual types and optimise the vulcanisation process. Thiuram-based accelerators are often used as secondary accelerators.

4. Are there environmentally friendly alternatives to conventional accelerators?

The elastomer industry is continuously researching more environmentally friendly alternatives to conventional accelerators in order to reduce their environmental impact. The focus is particularly on replacing toxic substances and reducing VOCs (volatile organic compounds).

Accelerators are indispensable components in elastomer processing, as they speed up the vulcanisation process and optimise the mechanical properties of the end product. Their targeted use lowers production costs, increases efficiency and makes it possible to produce rubber seals that meet high demands for durability and load capacity. Whether in tyres, technical rubber products or profiles, accelerators play a central role in compound production.