Recycled plastic data sheets: what to check (MFI, moisture, fillers)

Key takeaway: For recycled plastic, a data sheet is only useful if it reports real ranges, test methods and a lot number. The three values that prevent the most problems on the machine are melt flow index (MFI), moisture and filler content; always check them against what your process needs.

A recycled plastic data sheet looks a lot like one for virgin resin, but you read it differently. With virgin material, values are typical and stable; with recycled material, every lot can move within a range. Knowing what to check lets you accept material with confidence or catch a problem lot before it reaches production.

If your quality system was built around virgin resin from global producers, this is where recycled material challenges a few assumptions. One practical note for plants in Mexico: local suppliers will usually call these documents ficha técnica (data sheet) and certificado de análisis (certificate of analysis).

Data sheet vs. certificate of analysis

They're two different documents, and you need both:

• Technical data sheet (TDS): describes a material grade: polymer, format, typical properties, test methods and processing recommendations.
• Certificate of analysis (COA): reports the results measured on one specific lot, with its lot number and date.

With virgin resin, many plants work from the data sheet alone. With recycled material, the lot certificate is what protects your process, because it describes the material you'll actually load into the hopper.

A useful data sheet includes, at minimum: polymer and grade identification, source (post-industrial or post-consumer), format (regrind or pellets), each property with its test method and conditions, ranges instead of single values, and a document date or revision.

Melt flow index: what it measures and how to read it

Melt flow index (MFI, also MFR) is the mass of molten polymer, in grams, that flows through a standard die in 10 minutes at a defined temperature and load. It's measured with methods such as ASTM D1238 or ISO 1133 and reported in g/10 min.

Test conditions vary by polymer: polypropylene is commonly tested at 230 °C with 2.16 kg, and polyethylene at 190 °C with 2.16 kg. Only compare values measured under the same conditions.

How to read it:

• High MFI: the material flows easily and generally has lower molecular weight. It suits thin-wall injection molding and long flow paths.
• Low MFI: higher viscosity and melt strength. That's what profile, sheet and pipe extrusion and blow molding need.

With recycled material, watch two effects. First, reprocessing can shift MFI: in polypropylene it tends to rise because of chain scission. Second, blending different grades yields an average MFI that may look fine on paper but hide erratic behavior on the machine. That's why you should ask for the range across several lots, not a single value.

Moisture: why it matters and how it's measured

Not all plastics react to water the same way:

• Hygroscopic: nylon (PA6, PA66), PC, PET, ABS and PC/ABS absorb moisture into the material.
• Non-hygroscopic: PP, PE and PS only hold surface moisture.

In nylon, PC and PET, processing wet material causes hydrolysis: water breaks polymer chains in the melt, viscosity drops and parts become brittle. In ABS the problem is usually cosmetic: splay and bubbles. Limits depend on the polymer; for nylon, producers commonly recommend processing below roughly 0.2%, and limits for PC and PET are much lower.

Two common methods:

• Karl Fischer titration: measures water specifically and is the most accurate.
• Loss-on-drying analyzer: faster, but it measures all volatiles, not just water.

Regrind has more exposed surface than pellets, so it picks up moisture faster. Make sure it arrives in sealed packaging and dry it before processing. We explain how the industrial desiccants inside resin dryers work in a separate guide.

Filler content: glass fiber and minerals

Many engineering plastics contain fillers or reinforcements: glass fiber, talc, calcium carbonate or other minerals. The naming tells you: PA66 GF30 contains 30% glass fiber by weight.

Actual content is verified with an ash test (ASTM D5630 or ISO 3451): the sample is burned off and the inorganic residue corresponds mainly to the filler. Density is a quick cross-check, because filled materials are heavier.

Why it matters with recycled material:

• In reinforced grades, grinding and reprocessing shorten the glass fibers, so stiffness and strength may fall below the original grade.
• Mixing filled and unfilled material produces erratic properties and inconsistent shrinkage.
• Fillers increase screw and barrel wear, which matters if your equipment isn't built for it.

That's why your supplier should keep the two streams separate. If you work with polyamides, our comparison of Nylon 6 vs. Nylon 66 explains what to expect from each.

Other values worth checking

What to do when a value doesn't add up

An out-of-range value doesn't always mean rejecting the lot, but it should trigger questions:

• Higher MFI than expected: were there extra reprocessing cycles, a blend with another grade or degradation from moisture?
• High moisture: did the packaging arrive damaged, or was the material stored outdoors? Drying often fixes it if your equipment allows.
• Ash content different from what's declared: filled and unfilled material may have been mixed, or the fiber content may differ.
• Density out of range: suspect another polymer in the blend.

Document the finding, compare it with the retained sample from the previous lot and ask the supplier for its analysis before you decide.

Lot acceptance checklist

1. Polymer and grade match your specification.
2. Every value states its test method and conditions.
3. The data sheet reports ranges and the certificate matches the lot received.
4. MFI falls within the range your process tolerates.
5. Moisture is within the limit, or you have enough drying capacity.
6. Ash and density confirm the declared filler content.
7. You keep a retained sample from each lot in case of a claim.

If you plan to blend the material with virgin resin, this review is the first step in the method for adding recycled content to production.

Next step

Zikloa's raw materials catalog includes virgin grades and materials for reprocessing, such as virgin Nylon 66, filled virgin Nylon 6, filled and unfilled nylon for reprocessing, extrusion-grade ABS and PC/ABS. If you need to confirm technical parameters before you buy, send us the specification you're looking for and we'll review the available material information with you.