In advanced polymer engineering, Coated Calcium Carbonate ( CaCO 3 ) is increasingly viewed not as a filler, but as a functional impact modifier. However, selecting the right grade requires looking beyond basic whiteness and checking the "invisible" metrics that define the longevity of the final product.
The Critical Role of D98 (Top Cut)
Most Technical Data Sheets (TDS) highlight the average particle size ( D 50 ). However, for high-pressure PVC pipes or thin-film plastics, the Top Cut ( D 98 )—the size of the largest particles—is the true reference point for failure.
The Stress Concentration Effect: An uncoated or poorly coated large particle acts as a "stress concentrator." Under tension, the polymer pulls away from this large rock, creating a void.
The Coating Solution: A uniform stearic acid coating allows the polymer to slide over the particle during impact, dissipating energy rather than cracking. If the coating coverage is uniform, Coated Calcium Carbonate actually increases the impact strength of rigid PVC, effectively turning a stone into a shock absorber.
Economics Beyond more info Price: The OAN Factor
A metric frequently overlooked by procurement teams is Oil Absorption Number (OAN).
Raw Calcium Carbonate is porous and absorbs liquid additives. In a PVC or masterbatch formulation, uncoated carbonate will "drink" expensive stabilizers, plasticizers, and processing aids, rendering them useless.
The Hydrophobic Shield: High-quality Coated CaCO 3 has a significantly lower OAN (typically 14-16 ml/100g compared to 20+ for uncoated).
The Cost Saving: By blocking the pores, the coating ensures that your expensive additives remain active in the polymer matrix. This means you can often reduce the dosage of expensive modifiers by simply switching to a better-coated carbonate.
Weathering and Hydrolysis Resistance
In outdoor applications (like window profiles or siding), moisture is the enemy. Water molecules can penetrate the interface between the plastic and the filler, leading to "chalking" and degradation.
A hydrophobic coating provides a molecular seal. It prevents water from wicking into the composite material. This implies that Coated Calcium Carbonate is essential not just for processing, but for the 10-year warranty of construction materials. It prevents the filler from becoming the weak link where hydrolysis begins.
Summary
To treat Coated Calcium Carbonate as a commodity is to ignore its engineering value. It is a tool for modulus control, additive preservation, and crack inhibition. The highest ROI comes from analyzing the coating uniformity and the D 98 value, ensuring the mineral supports the plastic rather than disrupting it.