Sulphur vulcanisation is the classic — but many modern elastomers need a cleaner, more thermally stable cross-link. Benzoyl peroxide 75% is the organic peroxide that delivers it.
When most people hear "vulcanisation", they think sulphur. And for natural rubber and many general-purpose synthetics, sulphur curing is still the standard. But entire families of elastomers — silicone rubbers, EPDM, fluoroelastomers and specialty compounds — either cannot be cured with sulphur or perform significantly better with peroxide cross-linking. That's where BPO 75% comes in.
Sulphur vs peroxide: two different kinds of cross-link
| Property | Sulphur vulcanisation | Peroxide (BPO) cross-linking |
|---|---|---|
| Bond type | Polysulphidic (S–S) bridges | Carbon–carbon (C–C) bonds |
| Heat resistance | Moderate — sulphur bonds break down at elevated temperature | Superior — C–C bonds are thermally stable |
| Compression set | Higher — S–S bonds rearrange under sustained load | Lower — C–C bonds resist permanent deformation |
| Odour / blooming | Characteristic sulphur odour, potential bloom | Odour-free, no sulphur bloom |
| Colour stability | Can discolour light-coloured compounds | Colour-neutral — preferred for white and coloured goods |
How BPO cross-links rubber
The mechanism is the same free-radical process that makes BPO useful as a polymerisation initiator:
- › Heat breaks the O–O bond, generating two benzoyloxy radicals.
- › Each radical abstracts a hydrogen from an elastomer chain, creating a carbon radical on the polymer backbone.
- › Two adjacent carbon radicals couple, forming a direct C–C cross-link between polymer chains.
The result is a thermally stable, non-blooming, colour-clean vulcanisate — essential for seals, gaskets, O-rings and any elastomer part that must hold its properties at elevated temperature or in contact with food, pharma or automotive fluids.
Where peroxide curing is the only option
- › Silicone rubber — no unsaturated bonds for sulphur to react with; peroxide is the primary cure system.
- › EPDM for high-heat applications — engine mounts, radiator hoses, weather seals.
- › Food-contact and medical-grade elastomers — no sulphur odour or bloom.
- › White and pastel-coloured rubber goods — peroxide curing avoids the yellowing sulphur causes.
Why BPO 75%?
Rubber compounding is weight-sensitive. A higher-assay peroxide means more active initiator per kilo, which translates to smaller dose weights, less non-reactive filler in the compound, and more predictable cross-link density. BPO 75% is the grade designed for exactly this: maximum active content in a stable, handleable powder form.
Dhiraj Chemicals manufactures BPO 75% as a reliable, consistent-assay vulcanising agent for silicone, EPDM and specialty rubber compounds. Shipped in 20 kg UN-approved fibre-board boxes. Get a quote →