“Predispersed chemicals” (sometimes searched for as “predisposed chemicals”) is the term rubber compounders use for chemicals supplied already dispersed in a carrier, rather than as loose powders or liquids. Here is what they are, how they are made and why so many rubber factories now use them.

What are predispersed chemicals?

Predispersed chemicals are rubber compounding additives – accelerators, sulphur, zinc oxide, antioxidants, blowing agents and others – pre-mixed into a polymer binder at a high, fixed concentration. They are also known as polymer-bound masterbatches or polymer-bound predispersions. At Chemipat they are supplied in a dust-free form ready to add straight to the mixer.

How are they made?

The active chemical is blended with a compatible polymer such as EPDM, NR, SBR, NBR or CPE, plus processing aids where needed, under controlled conditions until fully wetted and dispersed. The batch is then formed into an easy-to-handle shape and checked for active content and dispersion quality.

Five reasons compounders use predispersed chemicals

1. Uniform quality. Pre-dispersion reduces batch-to-batch irregularities and undispersed specks.
2. Health and safety. Binding hazardous or dusty chemicals in polymer reduces worker exposure.
3. Less contamination. No powder drifting between mixing lines or settling on other compounds.
4. Accurate dosing. A known active content makes weighing simpler and more repeatable.
5. Faster mixing. Chemicals incorporate quickly, which can shorten cycle times.

Which chemicals are available predispersed?

• Accelerators – CBS, TBBS, MBTS, MBT, TMTD, TBzTD, ZDEC, ZDBC, DPG and others
• Vulcanizing agents – sulphur, insoluble sulphur and sulfur masterbatch, zinc oxide
• Sulphur donors – DTDM, DPTT, DPTH
• Antioxidants – MBI, MMBI, ZMMBI, NDBC
• Blowing agents, retarders, flame retardants and adhesion promoters

See the full list with CAS numbers on our predispersed chemicals page.

Where are they used?

Automotive components, tyres, cables, conveyor belting, hoses, flooring, inflatable goods, shoe soles and rubberised fabrics – essentially anywhere rubber additives are mixed into a compound.

Talk to a UK manufacturer

Chemipat is a family-run manufacturer based in Salford, producing predispersed chemicals since 1976. We also offer bespoke development and confidential toll manufacturing. Get in touch for samples or technical advice.

Accelerators are used in small amounts but have an outsized effect on how a rubber compound cures. That makes how you add them just as important as which ones you choose. In this guide we look at why many compounders switch from loose powder accelerators to an accelerator masterbatch, and how to make the change.

What does a rubber accelerator do?

Sulphur on its own vulcanizes rubber very slowly and at high temperature. Accelerators speed the reaction, lower the cure temperature and help build a more efficient cross-link network, improving tensile strength, compression set and ageing. Most compounds use a primary accelerator (a sulfenamide such as CBS or TBBS, or a thiazole such as MBTS) with a smaller dose of secondary accelerator (a thiuram, dithiocarbamate or guanidine) to fine-tune cure speed.

The problem with powder accelerators

• Dispersion: fine powders can agglomerate. Undispersed specks create local over- or under-cure.
• Dust: airborne accelerator dust is a health and housekeeping issue, and can contaminate other compounds in the mill room.
• Weighing accuracy: at dosages below 1 phr, small weighing errors become large percentage errors.
• Flow and storage: powders can cake, bridge in hoppers and carry static.

How an accelerator masterbatch helps

In a masterbatch, the accelerator is already dispersed in a polymer binder at a fixed active content – typically 70–80%. The result is a dust-free form that wets into the rubber quickly. Compounders typically see more consistent rheometer curves, cleaner working areas and simpler weighing. It is the same principle behind all polymer-bound masterbatches.

Which accelerator masterbatch should you choose?

The binder should suit your base polymer: E (EPDM), NR, SBR, NBR or CPE.

Converting a formulation

To keep the same amount of active accelerator, divide your powder dosage by the active fraction:

Masterbatch phr = powder phr ÷ (active % ÷ 100)

Example: 1.2 phr of powder CBS becomes 1.2 ÷ 0.8 = 1.5 phr of CBS 80E. The binder adds a small amount of polymer, which is rarely significant but worth noting in tight specifications. Always confirm cure on a rheometer after switching.

Need help?

Chemipat has manufactured predispersed rubber chemicals in Salford since 1976. We can recommend a grade, supply samples or develop a bespoke accelerator blend. Contact our team.