Acid by-products in CR and FKM
Halogenated elastomers release hydrogen chloride or hydrogen fluoride during cure. Without an effective acid acceptor, the acids degrade the polymer, attack moulds and disturb the cure rate.
Industry · Rubber
Magnesium Oxide, Desiccants and Fillers for Rubber Compounding
Activators, acid acceptors, moisture scavengers and mineral fillers for tyre and non-tyre rubber goods, tested batch by batch for compounders.
ISO 9001 certified processes
NABL-accredited lab testing
CoA, TDS & MSDS with every shipment
Export packaging worldwide
Overview
Minerals engineered for rubber
Magnesium oxide, desiccants and mineral fillers are working ingredients in rubber compounding, not passive additives, and each one is chosen to solve a defined problem in the mixing room or the curing line. Obsidian Minerals supplies MgO for chloroprene and fluoroelastomer cures, calcium oxide-based desiccants that help prevent porosity, and calcium and magnesium carbonate fillers for tyre and non-tyre rubber goods.
Each addresses a specific processing problem. Chloroprene (CR) and fluorocarbon (FKM) rubbers release acidic by-products during vulcanisation; MgO neutralises them, adjusts cure rate and provides scorch safety. Moisture carried in by fillers, oils and polymers turns to steam during curing and produces blisters and porosity, especially in continuous and low-pressure cures such as hot-air and salt-bath extrusion. Calcium oxide desiccants react with that water before it can cause defects. White fillers such as calcium carbonate and magnesium carbonate add volume, aid processing and support translucent or coloured compounds where carbon black cannot be used.
Our rubber range includes high activity and standard activity MgO, calcium oxide-based and molecular sieve desiccants, dual-function desiccant fillers, industrial grade magnesium carbonate and coated calcium carbonate. Each lot is tested in an NABL-accredited laboratory, and a TDS, MSDS/SDS and batch CoA accompany every shipment. Samples are available for rheometer, scorch and porosity trials.
Problems we help solve
Porosity and blistering
Residual moisture in compound ingredients vaporises during vulcanisation, leaving pores and blisters, especially in extruded profiles cured at atmospheric pressure. Scrap and rework rise quickly as a result.
Scorch and processing safety
Compounds that begin to cure in the mixer, on the mill or in the extruder barrel cannot be shaped properly. Activators must give a safe processing window and a consistent final cure.
Colour in white and translucent compounds
Light-coloured and translucent goods cannot use carbon black. Compounders need white fillers that add volume and process well without compromising appearance or key physical properties.
Recommended products for Rubber
Magnesium Oxide
High Activity Magnesium Oxide
Light-burned MgO with a surface area above 100 m²/g, acting as activator and acid acceptor in CR and FKM, and balancing scorch safety with efficient neutralisation of acidic cure by-products.
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Magnesium Oxide
Standard Activity Magnesium Oxide
Moderate-activity MgO for general rubber goods and less critical halogenated compounds, where a slower, more forgiving reaction rate suits the mixing and curing process used by the compounder.
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Desiccants
Calcium Oxide Desiccant for Rubber and Polymers
Calcium oxide-based desiccant that reacts irreversibly with moisture in the compound, helping to prevent porosity and blistering in EPDM profiles, hoses and other continuously cured goods.
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Desiccants Filler
CaO-based Desiccant Filler Grade
Dual-function CaO-based filler that scavenges moisture while contributing filler volume, simplifying formulations where both porosity control and mineral loading are needed in one ingredient added at the mixer.
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Magnesium Carbonate
Industrial Grade Magnesium Carbonate
Semi-reinforcing white filler with a refractive index close to that of natural rubber, used in translucent and light-coloured compounds such as shoe soles and moulded goods.
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Calcium Carbonate
Coated Calcium Carbonate (Stearic Acid Treated)
Stearic acid-treated calcium carbonate that disperses readily in rubber, used as an extending filler that aids extrusion smoothness and dimensional stability in non-tyre goods such as profiles and hoses.
View grade specsRubber — common questions
Why is magnesium oxide used in chloroprene rubber?
Magnesium oxide is used in chloroprene rubber as an acid acceptor and cure moderator. It absorbs the hydrogen chloride released during vulcanisation, which protects the polymer and the mould, and it delays the onset of cure to give scorch safety during processing. It is normally used with zinc oxide, with the MgO added early in mixing.
How do desiccants prevent porosity in rubber?
Calcium oxide-based desiccants react chemically with free moisture in the compound, forming calcium hydroxide and locking the water in place. Without them, that moisture turns to steam during curing and creates pores and blisters, particularly in hot-air, microwave or salt-bath cured extrusions. Desiccants are often supplied as dispersions or masterbatches for easier, dust-free mixing.
What dosage of calcium oxide desiccant is typical?
Dosage commonly falls in the range of about 3 to 10 phr, depending on how much moisture the fillers, oils and polymers carry, the cure method and the storage conditions of the compound. Compounds with high levels of mineral filler or recycled material may need more. Confirm the level by testing porosity and physical properties on cured samples.
Which filler suits translucent rubber compounds?
Magnesium carbonate is widely used for translucent and pale compounds because its refractive index is close to that of natural rubber, so the filled compound keeps much of its clarity at moderate loadings. Precipitated silica is often combined with it where more reinforcement is needed. Test loadings in your own compound to balance clarity against hardness.
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