Reading a Masterbatch CoA: The 7 Properties Every Buyer Should Check

MFI, ash content, moisture, colour delta-E, and dispersibility — a practical guide to reading a Certificate of Analysis before accepting a shipment.

A Certificate of Analysis (CoA) is a batch-specific quality document that confirms the tested properties of a masterbatch shipment meet the agreed specification. Every Blau Batch shipment comes with a CoA — but knowing how to read it is just as important as receiving it. This guide explains the seven key properties you should check on every CoA, what they mean, and what to watch for.

1. Melt Flow Index (MFI / MFR)

MFI (also called Melt Flow Rate, MFR) measures how easily the polymer flows when melted, expressed in g/10min. For FMPE, the test is typically run at 190°C / 2.16 kg; for FMPP, at 230°C / 2.16 kg (ISO 1133). MFI affects how the masterbatch blends with your base resin — a very high or very low MFI can cause processing problems. Check that the reported value falls within the range specified on your product TDS.

2. Ash Content

Ash content (ISO 3451) is the residue remaining after burning the organic polymer, expressed as a percentage by weight. For filler masterbatch, ash content is directly related to CaCO₃ loading — an 80% loading grade should show approximately 79–81% ash. A result significantly outside this range indicates either a production issue or a mismatch with the specified grade.

3. Moisture Content

Moisture content should be very low — typically below 0.2% for filler masterbatch. Elevated moisture causes processing defects including surface bubbles, voids, and visual surface defects (splay marks). This is particularly critical for blown film and injection moulding. If moisture is elevated, the material may need to be dried before use (typically 2–4 hours at 80°C for PE-based grades).

4. Colour / Appearance

For filler and white masterbatch, CoA may include a visual appearance notation (e.g., "white to off-white pellets, uniform colour"). For colour masterbatch, a ΔE value is critical — this measures the colour difference against a reference standard. A ΔE of ≤ 1.0 is generally imperceptible; Blau Batch colour masterbatch targets ΔE ≤ 0.5 batch-to-batch.

5. Dispersibility

Dispersibility is assessed by pressing a thin film of the blended compound and inspecting it against a light source for undispersed agglomerates (specks, gels, or hard particles). Poor dispersion is one of the leading causes of film defects and print quality issues. Request the dispersibility rating or filter pressure value (ΔP) if relevant to your application.

6. Density / Bulk Density

Higher CaCO₃ loading results in higher density — an 80% filler grade will have a density of approximately 1.6–1.8 g/cm³ versus approximately 0.92 g/cm³ for LDPE. This affects gravimetric dosing calculations. If you dose by weight, density consistency between batches ensures consistent dosage. Check that reported density is within the expected range for your grade.

7. Pellet Appearance & Uniformity

While not always a numerical test, the CoA should confirm pellet appearance — size, shape, and colour should be consistent with previous batches. Unusual discolouration (yellowing, dark specks) can indicate degradation during processing. Non-uniform pellet size can cause dosing inconsistencies. If something looks wrong visually, request a replacement or additional testing before processing.

What to Do if a Value is Out of Range

If any value on the CoA falls outside the agreed specification range, raise a non-conformance report (NCR) with your supplier before processing the batch. Processing out-of-specification material makes it much harder to claim a replacement or credit — and may cause downstream quality issues that are difficult to attribute. Blau Batch's quality claims process requires written notification within 14 days of delivery, accompanied by representative samples.

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