Sulphur-cured

Sulphur crosslinking is based on a chemical reaction between the polymer chains of the rubber and sulphur atoms. This creates disulphide and polysulphide bridges, which link the polymer chains together and increase the elasticity and resistance of the material.

Sulphur crosslinking process

• Step 1: adding sulphur and accelerators to the rubber compound.

• Step 2: heating the material to a temperature between 140 °C and 180 °C.

• Step 3: chemical reaction between sulphur and polymer chains, forming crosslink bridges.

• Step 4: cooling the material, which fixes the crosslinked structure.

Sulphur crosslinking gives the material specific properties that make it ideal for technical applications:

• Elasticity: high flexibility combined with dimensional stability.

• Mechanical strength: increased tensile strength and abrasion resistance.

• Thermal stability: good resistance to heat and cold.

• Chemical resistance: resistance to many chemicals and weathering.

• Longevity: reduced wear and longer product life.

Sulphur crosslinking is mainly used for unsaturated polymers, as these have double bonds, which are required for the crosslinking reaction:

Material	Properties	Typical applications
NR (natural rubber)	High elasticity and tensile strength	Tyres, seals
SBR (styrene-butadiene rubber)	Good abrasion resistance	Tyres, conveyor belts
EPDM	High weather and ozone resistance	Outdoor seals, sealing profiles
NBR (nitrile rubber)	Resistant to oils and greases	Hoses, O-rings

Sulphur crosslinking offers numerous advantages that make it indispensable in the rubber industry:

• Optimised material properties: improved elasticity, strength and resistance.

• Cost savings: efficient production of durable products.

• Wide range of applications: adaptable to different materials and uses.

Although sulphur crosslinking offers many advantages, there are also some challenges:

• Process control: precise control of temperature and time is required to achieve optimum results.

• Ageing: sulphur-cured materials can become brittle with prolonged use.

• Chemical limitations: not all polymers are suitable for sulphur crosslinking.

Sulphur-cured materials are used in numerous industries:

Automotive industry

• Tyres: high abrasion and temperature resistance.

• Seals: resistant to mechanical and thermal loads.

Mechanical engineering

• Conveyor belts: robustness and longevity under load.

• Hoses: resistant to pressure and chemicals.

Construction industry

• Sealing profiles: weather- and UV-resistant for windows and facades.

• Shock absorbers: elasticity to reduce vibration.

• Why is sulphur used for crosslinking? Sulphur creates strong crosslink bridges that improve the mechanical and elastic properties of the material.

• How does sulphur crosslinking differ from other crosslinking processes? Compared with peroxide crosslinking, sulphur crosslinking produces more flexible, more elastic materials.

• Which materials are not suitable for sulphur crosslinking? Polymers without double bonds, such as polyethylene (PE) or polypropylene (PP), cannot be sulphur-cured.

• How is sulphur crosslinking tested? By physical tests such as tensile strength, hardness and dynamic load testing.

Sulphur crosslinking is an established process in the rubber industry that produces materials with excellent elasticity, strength and resistance. It enables the manufacture of durable products that are indispensable in many industries. Despite its challenges, sulphur crosslinking remains a central process for optimising material properties.