What Is Accelerator CZ (CBS)?
Accelerator CZ, also known as CBS, CAS 95-33-0, chemically N-cyclohexyl-2-benzothiazolesulfenamide, is a sulfenamide (delayed-action) rubber accelerator. It is one of the most widely used accelerators in the rubber industry, above all in tyres, because it combines long scorch safety during processing with a fast, efficient cure once the temperature is raised.
Accelerators are the chemicals that make sulfur vulcanisation fast and controllable. Sulfenamide accelerators such as CZ are “delayed action”: they do not react quickly at mixing and forming temperatures, but they decompose briskly at cure temperature to release the active accelerator. This is what lets a compound be mixed, shaped and stored without premature vulcanisation, then cured quickly in the mould. PolyBlueChem supplies Accelerator CZ (CBS) to a controlled specification with per-batch COA and SDS.
| CAS number | 95-33-0 |
| Chemical name | N-Cyclohexyl-2-benzothiazolesulfenamide |
| Synonyms | Accelerator CZ; CBS; N-cyclohexylbenzothiazole-2-sulfenamide; CZ |
| Molecular formula | C13H16N2S2 |
| Molecular weight | 264.4 g/mol |
| Type | Sulfenamide accelerator (delayed action) |
| Appearance | Greyish white or light yellow powder |
Chemistry and Structure
Accelerator CZ is a sulfenamide: a benzothiazole ring (the same thiazole nucleus found in MBT and MBTS) is linked through a sulfur atom to a secondary nitrogen, which carries a cyclohexyl group. The structure explains the behaviour:
- The benzothiazole group is the “active” accelerator fragment. When released, it is essentially MBT, the classic thiazole accelerator.
- The sulfur-nitrogen bond is the “delay” mechanism. It is reasonably stable at processing temperatures but breaks readily at cure temperature – that is the delayed action.
- The cyclohexylamine fragment released on decomposition acts as an activator, so the accelerator is self-activating.
Because the active species is released only at cure temperature, CZ gives a good balance of processing safety (scorch) and cure speed. It is a medium-delay sulfenamide, between the faster primary thiazoles (MBT/MBTS) and the strongly delayed TBBS (NS) and DCBS.
How It Works: Delayed-Action Vulcanisation
In a sulfur cure, the accelerator controls how quickly and completely the rubber crosslinks. Sulfenamide accelerators work in stages:
- Processing (cool) – CZ is stable and does not significantly accelerate vulcanisation, so the compound can be mixed, extruded, calendered and stored without scorching.
- Heating to cure temperature – the sulfur-nitrogen bond of the sulfenamide breaks, releasing the benzothiazole fragment (MBT) and cyclohexylamine.
- Cure – the released thiazole, with the amine activator and the zinc oxide/stearic acid activator system, speeds the reaction of sulfur with the polymer, forming crosslinks.
- Completion – the crosslink density develops quickly, giving the desired physical properties.
A sulfur vulcanisation system is therefore not just the accelerator: it typically needs sulfur (the crosslinker), activators (zinc oxide and stearic acid) and, often, a secondary accelerator or retarder to fine-tune scorch and cure. CZ sits at the centre of that system in a great many compounds.
How Accelerator CZ Is Produced
Accelerator CZ is made by reacting 2-mercaptobenzothiazole (MBT) with cyclohexylamine in the presence of an oxidising agent, which forms the sulfur-nitrogen bond of the sulfenamide:
- MBT is dissolved or suspended with cyclohexylamine.
- An oxidant (for example, a hypochlorite or hydrogen peroxide system) couples the thiazole thiol to the amine, forming the sulfenamide.
- The product is filtered, washed and dried, then milled to a powder.
Process control targets the correct sulfur-nitrogen linkage and minimises residual MBT and amine, which would affect scorch, cure rate and odour. The specification therefore fixes melting point, heating loss, ash and sieve residue rather than only the assay.
Specifications and Quality Control
Accelerator CZ is supplied as a greyish white or light yellow powder to the following specification:
| Parameter | Specification |
|---|---|
| Appearance | Greyish white or light yellow powder |
| Initial melting point | 98 °C min |
| Heating loss | 0.30% max |
| Ash | 0.30% max |
| Sieve residue (100 mesh) | 0.1% max |
| Parameter | What it controls |
|---|---|
| Initial melting point (98 °C min) | Purity and identity; a low melting point signals impurities or residual MBT |
| Heating loss (0.30% max) | Moisture and volatiles; affects weighing and processing |
| Ash (0.30% max) | Inorganic residues |
| Sieve residue (100 mesh, 0.1% max) | Particle size / dispersion in the compound |
A specification sheet and a per-batch certificate of analysis (COA) are available on request.
Key Properties
| Property | Behaviour | Practical value |
|---|---|---|
| Type | Sulfenamide, delayed action | Scorch safety + fast cure |
| Form | Powder | Easy to weigh and disperse |
| Delayed action | Stable at processing temperature | Safe mixing, extrusion and storage |
| Cure character | Fast, efficient once activated | Good physical properties at low level |
| Activators | Needs ZnO + stearic acid (and sulfur) | Standard sulfur cure system |
Applications
Accelerator CZ is used across tyres and technical rubber goods.
| Industry / product | Function |
|---|---|
| Tyres | Accelerator for tread, carcass and sidewall compounds |
| Belts and hoses | Cure control for conveyor and transmission belting, hydraulic hoses |
| Moulded goods | Seals, gaskets and mechanical parts |
| Footwear and general rubber | General-purpose delayed-action acceleration |
| Latex and adhesives | Where a delayed cure is wanted |
- Tyres – CZ is a standard sulfenamide for tyre compounds, giving the scorch safety needed for large components and the fast cure needed for productivity.
- Technical rubber goods – belting, hoses, seals and mouldings, where the balance of processing safety and cure speed is critical.
- General rubber – NR, SBR, BR and blends, activated with zinc oxide and stearic acid.
Accelerator CZ vs Other Accelerators
CZ is one of several accelerators; the choice turns on scorch safety, cure speed and the compound.
| Accelerator | CAS | Class | Delay | Typical role |
|---|---|---|---|---|
| MBT | 149-30-4 | Thiazole | Low (fast) | General accelerator; intermediate |
| MBTS | 120-78-5 | Thiazole (disulfide) | Low-medium | General accelerator, better scorch safety than MBT |
| CZ (CBS) | 95-33-0 | Sulfenamide | Medium | Tyres and technical goods |
| TBBS (NS) | 95-31-8 | Sulfenamide | Medium-high | Tyres; the most common sulfenamide |
| DCBS | 4979-32-2 | Sulfenamide | High | Thick sections, long scorch |
| DPG | 102-06-7 | Guanidine | Low (fast) | Secondary accelerator / activator |
Guidance: choose CZ for a balanced delayed-action accelerator; move to TBBS or DCBS when more scorch safety is needed (larger or thicker parts); use thiazoles (MBT/MBTS) where a faster, less delayed cure is acceptable; add DPG as a secondary accelerator to speed a thiazole or sulfenamide system.
Dosage and Cure Systems
Accelerator levels are set by the cure system and confirmed by cure testing. The figures below are orientation only.
| Cure system | Character | Accelerator use |
|---|---|---|
| Conventional (CV) | Higher sulfur, lower accelerator | Higher sulfur, moderate sulfenamide |
| Semi-efficient (semi-EV) | Medium sulfur, higher accelerator | More sulfenamide, less sulfur |
| Efficient (EV) | Low sulfur, high accelerator | High sulfenamide, minimal sulfur |
Because a sulfenamide needs sulfur and activators, the compound is balanced as a system: sulfur, zinc oxide, stearic acid, the sulfenamide, and often a secondary accelerator or retarder. The aim is the required cure rate, scorch safety and final crosslink density. Confirm the level by rheometer and physical tests.
Safety, Handling and Storage
- Skin sensitisation – like most rubber accelerators, CZ is a potential skin sensitiser (H317). Avoid skin contact; wear suitable gloves and follow good industrial hygiene.
- Dust – avoid breathing the powder; use local extraction where large amounts are handled.
- Nitrosamine awareness – sulfenamide accelerators based on cyclohexylamine (CZ) are preferred over those based on secondary amines where nitrosamine formation is a concern.
- Storage – keep sealed, cool and dry, away from acids and oxidisers.
Regulatory Status
| Use | Status (as commonly cited) |
|---|---|
| Rubber (industrial) | Governed by the buyer’s specification and article requirements |
| Food-contact / potable-water rubber | Only where the specific accelerator is permitted; confirm the applicable regulation |
Packaging, Logistics and Supply
| Item | Standard options |
|---|---|
| Packaging | 25 kg PP/PE bags or fibre drums |
| Documentation | Per-batch COA and SDS |
| Incoterms | FOB and CIF |
| Storage | Sealed, cool and dry |
As a specialty rubber chemical, price tracks the MBT and cyclohexylamine feedstock and the finishing quality. Buying on committed tonnage gives the best terms.
Sulfenamide Accelerators Compared (CZ, TBBS, DCBS)
The three common sulfenamide accelerators differ mainly in how strongly delayed they are, which sets the scorch safety and the cure behaviour.
| Accelerator | Amine component | Delay | Best for |
|---|---|---|---|
| CZ (CBS) | Cyclohexylamine | Medium | General tyres and technical goods |
| TBBS (NS) | tert-Butylamine | Medium-high | Tyres; most widely used sulfenamide |
| DCBS | Dicyclohexylamine | High | Thick sections, long scorch safety |
The trend is straightforward: the bulkier the amine, the more delayed the accelerator and the longer the scorch time. CZ sits in the middle – more delayed than the thiazoles (MBT/MBTS), less so than TBBS or DCBS. A formulator chooses within this family to match the shape and thickness of the article and the processing temperature.
Scorch Safety and the Processing Window
Scorch is premature vulcanisation – the compound starting to crosslink before it is shaped. It ruins the stock and can block the mixer, extruder or mould. The processing window is the difference between the temperature and time a compound can tolerate during processing and the point at which it begins to cure.
- Why CZ helps – as a delayed-action sulfenamide, CZ widens the processing window: the compound can be heated (during mixing and extrusion) without curing.
- What shortens the window – higher processing temperatures, longer residence times, more active cure systems, and some fillers/additives.
- How it is measured – the Mooney scorch test and the rheometer (cure curve) quantify scorch time and cure rate; the compound is adjusted until both are acceptable.
- When to change accelerators – if a compound scorches, a more delayed sulfenamide (TBBS, DCBS) or a retarder (such as PVI) may be needed; if it cures too slowly, a faster system is used.
CZ therefore earns its place in large and complex articles, where the time between mixing and cure is long and premature vulcanisation would be costly.
Nitrosamine Awareness
Some rubber chemicals can, under certain conditions, contribute to the formation of nitrosamines, which are a regulatory concern in rubber articles (especially those in contact with skin or in sensitive applications). The risk depends on the amine from which the accelerator is derived:
| Amine type | Nitrosamine potential | Examples |
|---|---|---|
| Secondary amines | Higher concern | Morpholine-based accelerators |
| Primary amines | Lower concern | CZ (cyclohexylamine), TBBS (tert-butylamine) |
Accelerator CZ is derived from cyclohexylamine (a primary amine), which is why it is generally regarded as a lower-nitrosamine option within the sulfenamide family. For applications with strict nitrosamine limits, the accelerator choice is made together with the rest of the cure system and confirmed against the applicable regulation.
Quality: Reading a CBS Certificate of Analysis
| Parameter | What it tells you |
|---|---|
| Initial melting point (98 °C min) | Confirms a pure, consistent sulfenamide; low values suggest residual MBT or impurities |
| Heating loss (0.30% max) | Moisture/volatiles; affects weighing and scorch behaviour |
| Ash (0.30% max) | Inorganic residues |
| Sieve residue (100 mesh, 0.1% max) | Dispersion; coarse material can leave undispersed spots and cure defects |
Because cure behaviour depends on the accelerator being pure and well dispersed, buying against a written specification and checking the batch COA is the practical way to keep cure consistency.
Accelerator CZ in Practice: Tyres and Technical Goods
CZ is chosen where a plant wants a balanced delayed-action accelerator that is easy to use across a range of compounds.
| Situation | Why CZ fits |
|---|---|
| Large components with a long build time | Scorch safety keeps the stock usable during assembly |
| Mixed production (several compounds) | Versatile, forgiving accelerator |
| Cure presses with limited time | Fast, efficient cure once activated |
| Light-coloured goods | Clean cure without discolouration |
In practice the formulator sets CZ against the sulfur level, activators and any secondary accelerator or retarder. A typical sulfur vulcanisation system pairs CZ with zinc oxide and stearic acid, elemental sulfur, and (where more speed or a different crosslink pattern is wanted) a secondary accelerator such as a thiuram or a small amount of DPG. The aim is a cure that is fast enough for productivity, safe enough for the processing window, and complete enough for the required physical properties. The level is confirmed by rheometer cure curves and by physical testing of the cured article.
Frequently Asked Questions about Accelerator CZ (CBS)
What is Accelerator CZ used for?
It is a sulfenamide (delayed-action) accelerator for sulfur vulcanisation, used mainly in tyres and technical rubber goods.
What is the CAS number of CBS?
95-33-0.
Is CZ the same as CBS?
Yes – CZ and CBS are two names for the same accelerator, N-cyclohexyl-2-benzothiazolesulfenamide.
Why is it called delayed action?
Because it stays largely inactive at processing temperature and only releases the active accelerator at cure temperature, giving scorch safety.
Does it need sulfur and activators?
Yes – it works in a sulfur cure system with zinc oxide and stearic acid as activators.
How does CZ differ from TBBS?
Both are sulfenamide accelerators; TBBS typically gives more scorch safety and is the most common tyre accelerator. CZ is a close, medium-delay alternative.
Is CZ a skin sensitiser?
Yes – like most accelerators it is a potential skin sensitiser; avoid skin contact.
Related reading
- Accelerator CZ (CBS) in rubber vulcanization
- Rubber antioxidants and accelerators: selection guide
- Accelerator TBBS (NS): properties and applications
- Accelerator MBTS (DM): properties and applications
- Accelerator CZ (CBS, CAS 95-33-0) – product page
PolyBlueChem supplies Accelerator CZ (CBS, CAS 95-33-0) to a controlled specification, with per-batch COA and SDS, competitive pricing on bulk volumes and FOB/CIF delivery. Contact us with your application, tonnage and delivery port.