About CaO-based Desiccant Filler Grade
The CaO-based Filler Grade is our general-purpose desiccant filler for rubber compounding. It combines calcium oxide with mineral carriers in a fine, free-flowing powder designed to be used at filler-type loadings. Compounders replace part of the whiting, clay or other mineral filler in the recipe, so that the filler package itself takes care of moisture removal.
This approach suits compounds with high mineral filler content, where moisture carried in by the fillers is the main source of porosity. Typical examples are EPDM sponge and dense profiles, general mechanical goods, flooring, rubber sheeting and moulded parts made with recycled crumb or reclaim. Instead of adding a separate concentrated desiccant, formulators adjust the filler split, which can simplify the recipe and the weighing step. The calcium hydroxide formed on reaction stays in the compound as a stable mineral.
Available CaO is typically in the range of 85–90 %, with particle size controlled for smooth dispersion in internal mixers and on mills. The grade can also be supplied as a masterbatch blend where dust control or pre-dispersion is preferred. Obsidian Minerals manufactures the CaO-based Filler Grade in Gujarat, tests available CaO, particle size and loss on ignition in an NABL-accredited laboratory and supplies each batch with a Technical Data Sheet and Certificate of Analysis.
Typical specifications
| Parameter | Typical Value | Test Method |
|---|---|---|
| Available CaO | 85–90 % | Internal method (titration) |
| Particle size, D50 | 5–12 µm | Laser diffraction |
| Residue on 45 µm | ≤ 2.0 % | Sieve |
| Loss on ignition (1000 °C) | ≤ 6.0 % | Internal method |
| Specific gravity | 3.0–3.3 | — |
| Appearance | White to off-white powder | Visual |
Typical values for guidance. Guaranteed limits are stated on the Technical Data Sheet and batch CoA. Masterbatch blend composition is confirmed at order.
Key features & benefits
Filler and drying agent combined
The CaO-based Filler Grade replaces part of the conventional mineral filler and removes moisture at the same time, so compounders control porosity without adding another ingredient to the recipe.
Suited to high filler loadings
Formulated with mineral carriers, the grade disperses well at the higher addition levels used in heavily filled rubber compounds, where a concentrated desiccant would be harder to distribute evenly.
Stable reaction product
Calcium oxide reacts with water to form calcium hydroxide, which stays in the vulcanisate as an inert mineral and does not release moisture again during cure or service.
Powder or masterbatch blend
Supplied as a free-flowing powder for standard mixing, or as a masterbatch blend that reduces dust and helps achieve uniform dispersion in short mixing cycles.
Applications
Heavily filled EPDM profiles
Used in sponge and dense EPDM extrusions with high whiting or clay content, where moisture from the filler would otherwise create porosity in hot-air or microwave continuous curing lines.
Mechanical goods and sheeting
Applied in general mechanical rubber goods, flooring and sheeting compounds to control moisture-related blisters while maintaining the total filler level and cost structure of the recipe.
Compounds with reclaim or crumb
Helps manage the variable moisture brought in by recycled rubber crumb and reclaim, reducing trapped-gas defects and improving surface quality in moulded and extruded parts.
Usage & handling
- Typical loading: 5–15 phr, replacing an equal or slightly lower weight of conventional mineral filler.
- Add with the fillers early in the mixing cycle to allow time for reaction with moisture.
- Check cure characteristics and hardness after the filler swap, as the grade is alkaline.
- Keep bags sealed in a dry store; reseal opened bags and use them promptly.
Packaging & supply
- 25 kg HDPE or paper bags; moisture-barrier liners on request
- 1 MT or 1.2 MT jumbo (FIBC) bags
- Custom and private-label packaging on request
Frequently asked questions
How much CaO-based Filler Grade should I use in a rubber compound?
Typical loadings are about 5–15 phr, replacing a similar weight of whiting, clay or other mineral filler. The right level depends on how much moisture the fillers, oils and polymer bring in, and on the cure method. Start in the middle of the range and adjust after checking porosity and properties.
Will replacing part of my filler change the compound properties?
Small replacements usually have a limited effect, but calcium oxide is alkaline and can influence cure rate and scorch with some cure systems. It also has a different specific gravity from most fillers, so compound density may shift slightly. A laboratory comparison of cure curves, hardness and tensile properties is recommended before production.
Is this grade suitable for PVC or sealants?
The CaO-based Filler Grade is designed mainly for rubber compounding. It can be trialled in PVC plastisols and less demanding sealants, but for moisture-curing sealants, adhesives and other critical systems we recommend the High-activity Grade, which has higher CaO content and a finer particle size.
What is the difference between the powder and masterbatch blend?
The powder is the most economical form and suits plants with good dust control. The masterbatch blend contains the desiccant filler pre-dispersed in a carrier, which reduces dust, improves dispersion in short mixing cycles and slows reaction with humid air before use. Carrier type can be discussed to suit your polymer.