Moisture in recycled and filled resins
Recycled polymers and mineral fillers carry moisture into the extruder. It vaporises in the melt, producing voids, lacing in film and splay on moulded surfaces unless it is removed.
Industry · Plastic & Polymer
Mineral Fillers and Additives for Plastics and Polymers
Calcium carbonate, dolomite, desiccants and magnesium oxide for PVC, polyolefins, masterbatch and thermoset compounds, with particle sizes developed to your process.
ISO 9001 certified processes
NABL-accredited lab testing
CoA, TDS & MSDS with every shipment
Export packaging worldwide
Overview
Minerals engineered for plastic & polymer
Mineral fillers and additives for plastics change both the cost and the performance of a compound. Obsidian Minerals supplies calcium carbonate, dolomite, desiccants and magnesium oxide to compounders, masterbatch producers and converters working with PVC, polyolefins and thermoset resins.
Fillers such as ground and coated calcium carbonate raise stiffness, improve dimensional stability and reduce shrinkage while replacing part of the polymer. Treating the surface with stearic acid makes the particle hydrophobic, so it disperses in the melt and picks up less moisture, which matters for thin films and high loadings. Desiccants address a separate issue: moisture in recycled resin or fillers causes voids, lacing and surface streaks during extrusion, and calcium oxide-based additives remove it before it can do damage. Magnesium oxide serves as an acid scavenger and stabiliser, and as a chemical thickener in unsaturated polyester moulding compounds.
Our polymer range includes standard, fine, precipitated and coated calcium carbonate, dolomite powder, calcium oxide, molecular sieve and silica gel desiccants, and magnesium oxide in two activity levels. All grades are tested in an NABL-accredited laboratory and supplied with a TDS and batch CoA. Custom particle sizes and coated grades can be developed with your technical team, and samples are available for compounding trials.
Problems we help solve
Filler dispersion at high loading
Untreated fillers agglomerate and absorb moisture, causing specks, weak spots and pressure build-up at screen packs. Dispersion becomes harder as filler loading increases in masterbatch.
Stiffness and dimensional stability
Unfilled polymers can warp and shrink unevenly as they cool. Mineral fillers raise modulus and reduce shrinkage, but only if particle size and purity are tightly controlled.
Acid scavenging and resin thickening
Halogenated polymers and some catalyst residues release acidic species, and polyester moulding compounds need a controlled thickening reaction. Both depend on a reactive oxide with consistent activity.
Recommended products for Plastic & Polymer
Calcium Carbonate
Coated Calcium Carbonate (Stearic Acid Treated)
Stearic acid-treated calcium carbonate for PVC pipe, profiles and polyolefin filler masterbatch, with a hydrophobic surface that disperses readily in the melt at high loadings.
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Calcium Carbonate
GCC Fine Grade Calcium Carbonate (D50 < 5 µm)
Fine GCC with a D50 below 5 µm for injection moulding, film and compounds where a finer particle supports surface finish and consistent dispersion in the polymer matrix.
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Dolomite
Dolomite Powder (200 / 325 Mesh)
Dolomite powder as a mineral filler in PVC, thermosets and polymer compounds, adding stiffness and density where a calcium-magnesium carbonate is preferred over calcite by the compounder.
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Desiccants
Calcium Oxide Desiccant for Rubber and Polymers
Calcium oxide-based desiccant that removes moisture from recycled polyolefins and filled compounds during extrusion, reducing voids, lacing and surface defects in film, sheet and moulded parts.
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Desiccants
Molecular Sieve Desiccant Powder
Molecular sieve desiccant for high-performance plastics and polyurethane systems, adsorbing moisture to very low levels where the reactivity or alkalinity of calcium oxide is unsuitable for the formulation.
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Magnesium Oxide
Standard Activity Magnesium Oxide
Moderate-activity MgO used as a chemical thickener in SMC and BMC and as an acid scavenger in polymer compounds, giving a predictable reaction rate during processing and maturation of the compound.
View grade specsPlastic & Polymer — common questions
Why use coated calcium carbonate in plastics?
Coating calcium carbonate with stearic acid makes the particle surface hydrophobic and compatible with the polymer. The filler then disperses more easily in the melt, absorbs less moisture and reduces torque and pressure during compounding. This allows higher filler loadings in PVC, polyolefin masterbatch and film with fewer specks and better surface quality.
How do desiccants help with recycled plastic?
Recycled polymers often carry moisture from washing, storage or contamination. In the extruder that water turns to steam, causing voids, lacing in blown film and surface defects in moulded parts. Calcium oxide-based desiccants, usually added as a masterbatch, react with the moisture in the melt so that it cannot form bubbles in the product.
What is magnesium oxide used for in polymers?
Magnesium oxide is used as an acid scavenger and stabiliser in halogen-containing polymers and some catalyst systems, and as a chemical thickener in unsaturated polyester sheet and bulk moulding compounds. In SMC and BMC it reacts with the resin to raise viscosity over a controlled maturation period, so that the compound can be handled and moulded.
Can you match the particle size of our current filler?
In many cases, yes. Custom particle sizes and coated grades can be developed with customers. Send us the specification or a sample of your current filler, with details of the polymer, process and loading, and we will compare it with our standard grades and advise whether a standard or custom grade fits.
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Talk to a plastic & polymer specialist
Describe your process and current material. We will recommend a grade, share the datasheet and arrange samples for trial.