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Air retention is the one performance claim every tire buyer can measure without a laboratory: the tire either holds pressure over a season or it does not. For compounders, that claim is decided long before the tire is built, in the choice between a general-purpose butyl for inner tubes and a halogenated butyl for the inner liner, and in whether the cure system you pair with that grade actually develops the network the grade was designed for. This guide sets out how to choose between IIR1953, BIIR2828 and CIIR1338 for air-retention work, and what to measure before you commit a production batch.
An Inner Tube and an Inner Liner Ask Different Things of the Same Polymer Family
Both parts exist to slow air down, which is why both sit in the butyl family: the polymer backbone is densely packed with side methyl groups that restrict gas diffusion, and that is the property the whole application rests on. Beyond that single shared mechanism, the two parts are manufactured and loaded in completely different ways, and a grade chosen for one will disappoint in the other.
An inner tube is a thick-walled, shaped article. It is extruded or calendered, spliced into a closed loop, and cured in a press or autoclave. The failures that reach the customer are typically a weak splice, porosity that shows up as a slow leak, or a tube that takes a permanent set and rubs through. What the compound needs is green strength to hold shape before cure, splice adhesion that survives inflation cycles, and enough cure latency that the compound does not start to scorch while it is still being handled.
An inner liner is a thin calendered sheet bonded directly to the carcass, cured as part of the tire. It has no splice to fail, but it has gauge, dispersion and adhesion to protect. A thin sheet exposes any undispersed filler or volatile pocket as a leak path, and it must co-vulcanize with the adjacent carcass compound rather than forming a weak interface. The compound needs flow at low shear so it can be calendered thin without defects, and tack so it survives building.
| Requirement | Inner Tube | Inner Liner |
|---|---|---|
| Form and gauge | Thick-walled extruded or calendered tube, spliced closed | Thin calendered sheet, bonded to carcass and cured with the tire |
| Dominant failure mode | Splice separation, porosity, permanent deformation | Leak through thin gauge, blisters, poor adhesion to carcass |
| Property priority | Green strength, splice strength, heat aging | Low-shear flow, filler dispersion, tack and co-cure |
| Typical grade logic | General-purpose butyl, sulfur cured | Halogenated butyl, faster cure, blendable with natural rubber |
The Three Grades and the Numbers That Separate Them
Chambroad Sinopoly's butyl range covers both sides of this split. The three grades most used in air-retention work, with the values stated in the company's submitted grade documentation:
| Grade | Type | Mooney ML(1+8) 125°C | Unsaturation | Volatile Matter | Position in the Range |
|---|---|---|---|---|---|
| IIR1953 | General-purpose butyl | 51.0 ± 5.0 | 1.70 ± 0.2 | ≤ 0.3 wt% | Tire inner tubes |
| BIIR2828 | Brominated butyl | 32.0 ± 4.0 | Not specified | ≤ 0.50 wt% | Tire inner liner |
| CIIR1338 | Chlorinated butyl | 38.0 ± 4.0 | Not specified | ≤ 0.50 wt% | Tire inner liner |
One procedural point before the numbers: treat the signed grade sheet in your qualification file as the governing document, and ask for the current revision with every quotation. Published web copy, a sales datasheet and the signed sheet are not always the same revision, and for a tire compound the difference between a 51 and a 50 Mooney centre is enough to shift your mixing energy and your cure curve.
What Each Number Predicts on Your Line
Mooney viscosity sets the processing window
Mooney is the single most useful number in the table because it predicts two things at once: how the compound behaves in your equipment and how much variation you can expect between deliveries. A 32 Mooney grade flows at low shear, which is what a thin liner sheet needs; it also accepts higher filler and oil loading before the compound becomes unprocessable, which is how liner compounds reach the stiffness a tire builder wants without losing calender performance. A 51 Mooney grade develops green strength much earlier, which is what a thick tube profile needs to hold dimension and survive splicing.
The tolerance around the centre matters as much as the centre itself. A ± 4.0 window on a 32 Mooney grade is roughly twelve percent of the target; the same absolute band on a 51 Mooney grade is under eight percent. If your process is sensitive to viscosity, ask for the batch trend rather than the specification limit, and compare your own incoming Mooney against it for at least five consecutive deliveries before you release the supplier.
Unsaturation sets the cure chemistry
IIR1953 carries 1.70 ± 0.2 unsaturation. That number is the count of double bonds available to a sulfur cure, so it determines how fast the compound crosslinks, how much accelerator you need, and how tight the final network is. Run it low within the window and the tube cures slowly and may not reach full modulus in the press cycle; run it high and you gain cure speed at the cost of some heat-ageing resistance. For a thick inner tube, where the inside of the wall is always the last part to reach cure temperature, this is the number that decides whether your cycle time is safe.
Halogenated grades do not rely on that path. The allylic halogen on BIIR2828 and CIIR1338 is the reactive site, which is why they cure faster than general-purpose butyl, why they can be co-vulcanized with natural rubber in a blended liner, and why the cure system you choose for them looks different from a tube recipe.
Volatile matter is a defect predictor, not a formality
Residual volatiles become gas at cure temperature. In a thick tube the gas has somewhere to go; in a thin calendered liner sheet it does not, and the result is a blister or a micro-porosity that reads as a slow pressure loss months later. This is why the volatile limit deserves a batch value rather than a check mark: ask what the actual figure was on the lot you are receiving, not only whether it met the limit. The same residual volatiles also add to the corrosion load on your downstream equipment, which is worth tracking if you run tight temperature control on the calender.
Choosing Between the Three for a Given Tire Program
IIR1953 for inner tubes
Take the general-purpose grade when the part is a standalone air chamber: truck and bus tubes, agricultural and off-road tubes, motorcycle and scooter tubes. The higher Mooney gives the extruded profile the green strength to hold shape through splicing, the unsaturation gives you a conventional sulfur cure you can tune with your existing accelerator package, and the tighter volatile limit suits a thick section where you want predictability rather than maximum filler loading. Full details sit on the IIR1953 grade page.
BIIR2828 for thin-gauge inner liner
This is the grade to start with when your liner is calendered thin and heavily filled. At 32 Mooney it is the lowest-viscosity grade in the group, so it disperses filler more readily and flows into a thin sheet with fewer surface defects, and the brominated cure site lets you build a resin-cured or sulfur-cured system that bonds to the carcass instead of sitting on top of it. Chambroad describes the line as running under advanced process control, which is the claim to test with batch-to-batch Mooney and tensile data rather than accept at face value.
CIIR1338 where cure simplicity and heat ageing dominate
The chlorinated grade sits between the two on viscosity at 38 Mooney and brings a different advantage: it cures on zinc oxide alone, without sulfur or a resin system, which simplifies the recipe and removes a class of cure-balance problems. It is also the grade to prefer where the liner or an adjacent part sees sustained heat, since chlorobutyl vulcanizates hold their properties well under long-term thermal load. If you are weighing the two halobutyl routes against each other, the practical difference is cure architecture and heat history rather than air retention, which is close between them.
| If your situation is | Start with | Because |
|---|---|---|
| Thick standalone tube, existing sulfur cure line | IIR1953 | Green strength and predictable sulfur cure in a thick section |
| Thin, highly filled liner sheet on a calender | BIIR2828 | Lowest viscosity, easiest dispersion, flexible cure architecture |
| Liner or adjacent part under sustained heat, simple recipe preferred | CIIR1338 | Zinc oxide cure without sulfur or resin, strong heat ageing |
| Blend with natural rubber for building tack | BIIR2828 or CIIR1338 | Halogenated grades co-vulcanize across the blend interface |
Need a grade sheet and a sample to run against your current compound? Send our rubber team the application, target gauge and cure system, and the response will be a specific grade recommendation rather than a catalogue.
The Cure System Decides Whether the Grade Works
Most disappointing butyl trials are not grade failures. They are cure mismatches, where a correctly specified polymer was crosslinked on a system designed for a different chemistry.
- General-purpose butyl on sulfur. The cure depends on the unsaturation in the chain, so the accelerator package and the grade's double-bond content have to be tuned together. Under-cure in a thick tube shows up as low modulus, high permanent set and a splice that creeps; the fix is usually thermal, not chemical.
- Bromobutyl on zinc oxide with sulfur or resin. The brominated site reacts far faster than a double bond, which buys you shorter cycles and co-vulcanization with natural rubber, but leaves less scorch safety. Resin-cured systems trade a little cure speed for higher green strength and better heat resistance, which suits liner compounds that must hold tack on the building drum.
- Chlorobutyl on zinc oxide alone. The simplest system available, and the easiest to get wrong in mixing: zinc oxide starts the cure on contact at temperature, so it goes in late in the cycle with the mixer running cool. Add it early and you will see scorch in the compound rather than in the tire.
If you blend halobutyl with natural rubber for tack, treat the cure balance as a two-phase problem. The two phases cure at different rates through different mechanisms, and a compound that looks fully cured on a rheometer can still have an under-cured halobutyl phase that leaks. Cure state at the interface is what your adhesion test is actually measuring.
What to Measure Before You Approve a Batch
A grade sheet tells you what the supplier intends to ship. Only your own measurements tell you what arrived. Build the approval sequence around these seven checks:
- 1. Mooney on arrival. Run ML(1+8) at 125°C against the grade window and log it against the supplier's certificate, delivery after delivery.
- 2. Rheometer curve in your recipe. Not the supplier's recipe. Record scorch time, t90 and minimum and maximum torque at your plant's cure temperature, and compare the curve shape rather than only the endpoints.
- 3. Permeability on your own cured sheet. This is the property the whole application exists for, so measure it on a sheet you cured to your own cycle, using the gas-permeability method your laboratory is accredited for. A datasheet figure generated on a different cure will not predict your liner.
- 4. Filler dispersion. Cut a section and inspect it, or run the dispersion rating your plant already uses. Undispersed black is the most common cause of a liner that leaks in one location and not another.
- 5. Green strength and tack. Pull a strip off the building drum and see how it behaves. For thin liner compounds, tack loss between mixing and building is a scheduling problem that shows up as a quality problem.
- 6. Splice or peel strength. Tubes get a splice test; liners get a peel test against a carcass compound. Both should be run on aged specimens as well as fresh ones.
- 7. Heat ageing. Hold cured specimens at elevated temperature and re-measure tensile and hardness retention. This is where a viscosity grade at the edge of its window usually reveals itself.
Supplier Verification for Tire-Grade Butyl
Tire makers sit inside automotive quality expectations even when they sell into the aftermarket, so the management-system side of a butyl supplier is not paperwork for its own sake. Chambroad Sinopoly's submitted documentation lists quality certification to IATF 16949 and ISO 9001, together with environmental, occupational health and safety and energy management certification for the butyl and halobutyl plants:
| Management System | Standard | Certificate Number |
|---|---|---|
| Quality | IATF 16949 and ISO 9001 | Listed for butyl and halogenated butyl rubber |
| Environment | ISO 14001 | 00225E33461R2M |
| Occupational health and safety | ISO 45001 | CQM25S23270R2M |
| Energy | ISO 50001 | 00225EN0790R1M |
Verify the scope statement on each certificate against the grade you are buying, and check validity dates rather than accepting a PDF without a date. Beyond certificates, four questions separate a polymer producer from a trader with a warehouse:
- Who owns the process? A producer can explain its own polymerisation and halogenation route and what it does about residual volatiles; a trader cannot.
- What does batch-to-batch data look like? Ask for the last twenty Mooney and volatile results as a trend, not a single certificate, and look at the spread inside the specification window.
- How is contamination controlled? Bale wrapping, anti-tack agent, metal detection and the segregation of grades through the line. A single metal fragment in a liner sheet is a tire failure.
- What is the change-notification clause? For an automotive supply chain, written notice of process or formulation change is the clause that protects your PPAP file when the supplier's plant evolves.
An RFQ That Gets a Usable Answer
Paste these into your first enquiry and you will get comparable responses instead of brochures:
- Part and application: inner tube or inner liner, tire category, target gauge, annual volume.
- Cure system you run today, and the equipment you will process on.
- Grade and Mooney window you are targeting, with the reference grade you use now.
- Required documents: current grade sheet with test methods, batch certificates, management-system certificates with scope, change-notification terms.
- Samples: quantity, delivery form and bale size for a trial run on your own line.
- Commercial terms: packaging, marking, delivery basis, and the lead time for repeat orders.
The wider butyl and halobutyl range, including shoe-sole and pharmaceutical grades that share the same production line, is listed in the rubber products section. If you are still separating the chemistry from the application, the site's article on butyl versus halogenated butyl covers the structural differences, and the automotive tire section lists the related materials.
Choosing a Grade for Air Retention?
Send your application, target gauge and current cure system. Our team will come back with the grade recommendation, the current grade sheet and sample terms for your own trials.
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