About Calcium Oxide Desiccant for Rubber and Polymers
Our calcium oxide desiccant is a finely milled, high-purity quicklime designed to be added in small amounts to rubber and polymer compounds. It reacts with free water to form calcium hydroxide, binding the moisture chemically so that it cannot be released again as steam during vulcanisation or moulding. Theoretical water uptake is about 32 % of the weight of calcium oxide present.
The grade is most often used in EPDM, NBR, CR and SBR compounds that are extruded and cured continuously in hot air, microwave, salt bath or steam. In these processes the compound is cured at atmospheric pressure, so any moisture from carbon black, mineral fillers, process oils or the polymer itself forms bubbles. A dose of calcium oxide removes this water during mixing and storage and gives a dense, smooth profile, tube or hose.
We supply the grade as a fine powder or as a masterbatch in which the calcium oxide is pre-dispersed. The masterbatch form reduces dust, protects the oxide from early reaction with air and helps it distribute evenly in internal mixers and two-roll mills. Obsidian Minerals produces this calcium oxide desiccant in Gujarat and tests available CaO, particle size and residue in an NABL-accredited laboratory, with a Certificate of Analysis for every batch.
Typical specifications
| Parameter | Typical Value | Test Method |
|---|---|---|
| Available CaO | ≥ 90 % | Internal method (titration) |
| Particle size, D50 | 3–8 µm | Laser diffraction |
| Residue on 45 µm | ≤ 1.0 % | Sieve |
| Loss on ignition (1000 °C) | ≤ 4.0 % | Internal method |
| Specific gravity | Approximately 3.3 | — |
| Masterbatch CaO content | On request | — |
Typical values for guidance. Guaranteed limits are stated on the Technical Data Sheet and batch CoA. Masterbatch carrier and active content are confirmed at order.
Key features & benefits
Chemical, irreversible drying
Calcium oxide desiccant converts water into calcium hydroxide, a stable solid. Unlike physical adsorbents, it does not release the captured moisture again at the high temperatures reached during vulcanisation.
Fine particle size
Milling to a D50 of a few microns gives a large reactive surface and reduces the risk of visible specks or surface roughness on extruded profiles, hoses and thin moulded parts.
Powder or masterbatch supply
The masterbatch form pre-disperses the oxide in a carrier, cutting dust, slowing reaction with humid air in the store and making dosing easier on automatic weighing systems.
Stable at compounding temperatures
The grade stays stable through mixing, extrusion and cure, and does not react with the polymer or common cure systems, so it can be added without changing the base formulation.
Applications
EPDM extruded profiles
Used in sponge and dense EPDM profiles, window and automotive seals cured in hot air or microwave lines, where moisture would otherwise cause porosity and poor surface finish.
Hoses and cable compounds
Added to hose covers, tubes and cable sheathing compounds that are cured continuously, helping produce dense, void-free walls and more consistent electrical and mechanical properties from batch to batch.
Moulded rubber goods
Applied in compression, transfer and injection moulded parts made with moist fillers or recycled rubber, reducing blistering, flow marks and trapped-gas defects in the finished article.
Recycled polymer compounding
Dosed in compounding of recycled polyolefins and other polymers where residual moisture from washed feedstock causes foaming, splay or surface streaks in extruded or moulded products.
Usage & handling
- Typical dosage: 3–8 phr in rubber compounds; 1–3 % in polymer compounding, adjusted to moisture load.
- Add early in the mixing cycle with the fillers so the oxide has time to react with moisture.
- Use the masterbatch form where dust control or automatic dosing is a priority.
- Keep sealed and dry; calcium oxide reacts with water and releases heat, so avoid wet handling.
Packaging & supply
- 25 kg HDPE bags; moisture-barrier liners on request
- 1 MT or 1.2 MT jumbo (FIBC) bags
- Custom pack sizes and private-label packaging on request
Frequently asked questions
How does calcium oxide desiccant work in rubber?
Calcium oxide reacts with free water in the compound to form calcium hydroxide. The water is chemically bound and does not turn to steam during cure. This is especially useful in continuous vulcanisation at atmospheric pressure, where there is no mould pressure to suppress bubbles from moisture in fillers, oils or polymer.
What is the typical dosage of calcium oxide in EPDM?
Most EPDM extrusion compounds use about 3–8 phr of calcium oxide, depending on filler and oil moisture, curing method and plant humidity. Compounds with high carbon black or mineral filler loadings, and those cured in hot air or microwave lines, usually need the higher end. Trials should confirm the minimum effective level.
Should I choose the powder or the masterbatch?
The powder is cost-effective and suits plants with good dust extraction and quick use of opened bags. The masterbatch is easier to handle, gives less dust, disperses more readily in short mixing cycles and is better protected against early reaction with humid air. Many compounders move to masterbatch for automotive and export work.
How is this different from the Desiccants Filler product?
This grade is a concentrated moisture scavenger used at low dosage purely to remove water. Desiccants Filler combines calcium oxide with mineral carriers and is used at higher loadings in sealants, PVC and rubber, where it adds filler volume while also scavenging moisture. Choose based on whether you need drying alone or both functions.