How do you read a PET flake specification?
Two lots of “clear hot-washed flakes” can behave very differently on a fiber or sheet line. The difference is in the numbers on the specification — and in how they were measured.
A PET flake specification is a list of limits, usually in percent or parts per million (ppm). Each one protects your process from a specific problem. Here is what to look for — and why.
What do IV and moisture tell you?
Intrinsic viscosity (IV), in dl/g, reflects the length of the polymer chains. Bottle flakes typically start around 0.70–0.80 dl/g; fiber can work with less, while strapping and sheet need more. Moisture matters because PET hydrolyzes when it is melted wet, cutting chains and lowering IV — which is why flakes are dried before extrusion and why moisture is limited in the specification.
Which contaminants cause defects?
| Parameter | Why it matters |
|---|---|
| PVC | Degrades at PET processing temperatures, causing black specks and yellowing. Usually the tightest limit. |
| Polyolefins (PE/PP) | Come from caps and labels; they do not mix with PET and create unmelted particles and weak points. |
| Glue | Label adhesive causes yellowing and gels. Hot washing removes it far better than cold washing. |
| Metal | Can damage screws and filters and breaks filaments; removed by metal separators. |
| Paper and labels | Burn into dark specks and block filters. |
| Other colors | Change the shade of clear products; limited in clear grades. |
Which physical properties matter?
- Flake size (often 8–14 mm) affects feeding and drying; too many fines add dust and moisture.
- Bulk density affects how much fits in a big bag and a container — and therefore freight per tonne.
- Color grade (clear, light blue, green, mixed) sets the applications the lot can serve.
How do you know the numbers are reliable?
Ask how the values were measured and on which sample. A certificate of analysis tied to the lot number, photos of the actual bags and, for larger contracts, pre-shipment inspection by an independent company reduce the risk of a lot that looks right on paper but not on the line. Our PET flakes page lists typical limits for hot-washed clear flakes.
General information only — not legal, tax or investment advice. Market conditions and regulations change; confirm the details for your case.
