A Certificate of Analysis (COA) is the document that turns "recycled pellets" into a defined, buyable grade. But it is only useful if you can read it. Here is what each figure on a recycled PP or HDPE COA means, and how to use it to make sure the material will run on your machine and perform in your part.
A COA is a batch-specific test report: it states the measured properties of the exact lot you are buying. For virgin resin, a generic datasheet is usually enough because every batch is identical. For recycled material, feedstock varies, so a per-batch COA is what gives you confidence the grade is consistent. If a recycled supplier cannot provide one, you are buying blind.
The single most important number. Melt flow rate — also called melt flow index (MFI) — measures how easily the molten plastic flows under a set load and temperature, in grams per 10 minutes (ASTM D1238). It tells you whether the material suits your process: low MFR (high molecular weight) suits blow moulding and extrusion; high MFR (lower molecular weight) suits injection moulding. Match the MFR on the COA to your machine and part first — everything else is secondary.
Density (g/cm³) confirms the polymer type and grade. HDPE typically sits around 0.94–0.96 g/cm³; PP is lighter, around 0.90–0.91 g/cm³. A density outside the expected range can signal filler, contamination or a material mix-up.
Excess moisture causes splay, bubbles and voids in moulded parts. A COA showing low moisture — or a note that the material is dried before dispatch — means fewer surface defects and less pre-drying on your side.
Ash content (%) indicates inorganic fillers or residue. For most recycled grades you want this low and stable; a consistent ash figure batch-to-batch is a sign of well-sorted feedstock.
Recycled grades are specified by colour — black, grey, blue, green — and the COA or product code states which. Appearance notes (uniform pellet size, no visible contamination) matter for feeding and surface finish.
For structural parts, impact strength (e.g. Izod/Charpy) shows how the material handles shock. It is the property that most often separates a good recycled grade from a marginal one.
Here is what a typical injection-grade recycled HDPE COA looks like, with the kind of values you should expect to see:
| Property | Method | Typical value |
|---|---|---|
| Material | — | Recycled HDPE, injection grade |
| Colour | Visual | Black |
| Melt flow rate (MFR) | ASTM D1238 | ≈ 12 g/10min |
| Density | ASTM D792 | ≈ 0.952 g/cm³ |
| Moisture | Gravimetric | Low / dried |
| Ash content | ASTM D5630 | Low, consistent |
| Pellet form | Visual | Uniform, no contamination |
A blow-grade HDPE COA would read similarly but with a much lower MFR (≈ 1 g/10min) and higher molecular weight — see our guide on blow vs injection grade. Recycled PP would show a density near 0.90 g/cm³ and its own MFR band.
We test recycled PP and HDPE in-house at our Telok Gong, Klang plant — melt flow rate, density and impact strength — and a Certificate of Analysis is supplied with every product, with detailed test reports available on request. It is how we make sure the grade you order is the grade you receive, batch after batch.
Tell us the grade you need — we'll send specs, a Certificate of Analysis and a sample to trial.
