How to Read an rPET Flake COA
A plain-English guide to the numbers on a recycled PET Certificate of Analysis — IV, moisture, PVC and contamination.
Key takeaways
- Check every lot at the gate — a COA describes a sample, your line runs the whole delivery.
- Sample from several bags at different depths, never just the top of one bag.
- A simple water float test catches PP/PE caps and labels; it does not catch PVC.
- PVC and moisture are the two problems most likely to cost you breaks and rejects in fibre.
- Keep a retained sample from every lot — it settles disputes fast and fairly.
Faisalabad’s polyester fibre and yarn mills are the biggest users of recycled PET in Punjab. Most mills already know which specs matter — we covered them in rPET for polyester fibre mills and how to read an rPET COA. This guide is about the next step: what to do when the truck is at your gate, so that off-spec flake is caught before it reaches the extruder, not after the breaks start.
Why the gate check matters more than the paperwork
A certificate of analysis (COA) tells you how a sample from a lot tested. It is essential — but it cannot guarantee that every bag in a 20-tonne delivery is the same. Bottle supply changes week to week, and a single bag with PVC or wet flake can cause filter blockages, yarn breaks and colour spots across a whole production run.
A short, consistent routine at receipt protects you in three ways: it catches problems before they cost machine time, it gives you evidence if a lot must be rejected, and it tells your supplier exactly what you expect — which, over time, is the cheapest quality control there is.
Step 1: Check the delivery before you unload
- Match the paperwork. Lot number on the bags matches the COA and delivery note; grade (clear or coloured, hot-washed) matches your order.
- Look at the bags. Torn, wet or open bags are an immediate question. Flake that has been rained on will need extra drying — or rejection.
- Count and weigh. Number of bags and weighbridge weight against the delivery note.
Step 2: Take a sample that represents the lot
The most common mistake is testing a handful from the top of one bag. Contaminants settle and separate during transport, so the top of a bag is rarely typical. A practical routine:
- Pick bags at random from across the load — for example, one in every five to ten bags, from different positions on the truck.
- From each, take flake from the top, middle and bottom using a sampling spear or scoop.
- Mix these into one composite sample, then split it: one part for testing, one part sealed and labelled as a retained sample with the lot number and date.
Step 3: Five quick checks your QA team can do on site
| Check | How | What a problem looks like |
|---|---|---|
| Visual | Spread a weighed sample on a white tray under good light | Coloured flakes in a clear lot, label pieces, dirt, black specks, fines/dust |
| Float–sink | Stir a weighed sample in a bucket of water; skim what floats, dry and weigh it | Floating pieces are PP/PE (caps, rings, labels) — PET sinks |
| Moisture | Moisture analyser, or weight loss on drying | Readings above the agreed limit, or wet/damp feel in the bag |
| Heat screen for PVC | Heat a thin layer of flake in a lab oven or on a hot plate | Flakes that turn brown or black are a strong sign of PVC |
| Magnet & smell | Pass a magnet through the sample; note any unusual odour | Metal pieces; oil, chemical or sour smell from poorly washed material |
Record each result against the lot number. Over a few months these records show you — and your supplier — exactly how consistent the supply really is.
The PVC trap: why the water test isn’t enough
The float–sink test is excellent for caps and labels because PP and PE are lighter than water while PET is heavier. But PVC is also heavier than water, so it sinks with the PET and looks almost identical. That is why PVC is the contaminant that most often slips through — and in fibre production even a small amount can degrade the melt, blacken spots and block filters.
The heat screen above is a common way to spot it quickly: when heated, PVC degrades and darkens while clean PET does not. Treat it as a screen, not a measurement — if you see dark flakes, hold the lot and test properly. For the background on why PVC and PP/PE are the priority, see our fibre mill guide; for how hot washing helps remove glue and residues, see hot-washed vs cold-washed flakes.
Step 4: Know when to send it to the lab
Some properties cannot be judged on site. Send the retained sample for laboratory testing when:
- Intrinsic viscosity (IV) needs confirming — IV affects melt strength and spinning, and it needs a lab method. Check it on a new supplier’s first lots and periodically after that.
- The heat screen shows dark flakes and you need a PVC level in ppm.
- Your line shows unexplained breaks, filter pressure rises or colour problems after a new lot.
- You are qualifying a new supplier or a new grade.
Step 5: Agree acceptance rules with your supplier in advance
Most disputes happen because nobody wrote down what “acceptable” means. Before the first delivery, agree in writing:
- The grade and spec limits — moisture, PVC, PP/PE, colour, flake size — and which test method decides each.
- How sampling will be done and who keeps the retained sample.
- What happens to an off-spec lot — return, re-dry, re-sort or price adjustment — and within how many days you must report it.
- That each lot comes with a COA and lot number, so problems can be traced.
A supplier that is confident in its material will welcome these rules. One that resists them is telling you something. Our checklist for judging suppliers is in choosing an rPET flake supplier in Pakistan.
What this means when you buy from us
At Shahbaz Traders we sort, crush and hot-wash post-consumer bottles in Okara, with caps, labels and glue removed and PVC controlled. Every lot can come with a COA and TDS on request, and we are happy to send a sample before your first order so your QA team can run exactly the checks above. We deliver to mills across Faisalabad’s industrial areas, including M-3 Industrial City, the Faisalabad Industrial Estate, Sargodha Road and Jhang Road. More on our Faisalabad supply is on the Faisalabad page.
Want a sample to test first?
Tell us your grade, monthly volume and spec limits. We’ll send a sample with its COA and quote today’s rate delivered to Faisalabad.
Request a sample & quote WhatsApp usFrequently asked questions
How should a fibre mill sample an rPET flake delivery?
Take flake from several randomly chosen bags across the load — top, middle and bottom of each — mix them into one composite sample, then split it into a test sample and a sealed retained sample labelled with the lot number and date.
Does the water float test detect PVC in PET flakes?
No. The float test separates PP and PE (caps, rings, labels), which float, from PET, which sinks. PVC also sinks, so it stays with the PET. A heat screen — where PVC flakes darken — or a laboratory test is needed to find PVC.
Which rPET problems cause the most trouble in polyester fibre spinning?
PVC and moisture are the most damaging: PVC degrades the melt and causes black specks and filter blockages, and excess moisture lowers viscosity during extrusion, leading to breaks. PP/PE, dirt and inconsistent colour also cause defects.
Do I need to test IV on every lot?
Not usually. IV needs a laboratory method, so most mills confirm it on a new supplier’s first lots and then check periodically, while running quick on-site checks for visual quality, PP/PE, moisture and PVC on every lot.
Can Shahbaz Traders send a sample to a Faisalabad mill before an order?
Yes. Tell us your grade, volume and spec limits and we can send a sample with its COA so your QA team can test it before you place an order. We deliver bulk rPET flakes to mills across Faisalabad.
