PET flakes are what a PET bottle becomes about two thirds of the way through recycling: sorted, de-labelled, cut into small pieces, washed, dried, and separated by colour, but not yet melted. At that point it stops being waste and becomes a traded commodity with a price per tonne and a specification sheet attached.
That specification is the part most explanations skip. Two lots can look identical in a bulk bag and be worth very different money, because the buyer is not judging appearance. A fibre spinner and a bottle-to-bottle converter check different lines on the same sheet.
This article covers what is on that sheet, which numbers come from the recycling line and which from the purchase contract, and how a lot gets checked before anyone signs for it. For the material itself, see What Is PET Plastic.
PET flakes are washed, size-reduced bottle material sold by specification rather than by appearance.
What PET Flakes Are and Why They Trade on a Specification
PET flakes are post-consumer bottles sorted, de-labelled, crushed, washed, dried, and colour separated into a granular raw material. They are an intermediate, not an end product. Every buyer re-melts them, so flakes are priced on how predictably they behave in an extruder rather than on how they look.
This is why the trade runs on numbers. A bulk bag of clean PET flakes going to a staple fibre plant and the same bag going to a food-contact converter are physically similar, but the second buyer is paying for contamination and viscosity guarantees the first will not fund. It is worth noticing who asks: many people searching what are PET flakes already hold flakes and want to know where to sell them, or have a container arriving and want to know what to check.
Two lots can look identical in the bag. The specification sheet, not the appearance, sets the price.
The PET Flake Specification Sheet Line by Line
A PET flake specification has about seven lines on it. Some numbers are produced by the recycling line and can be quoted by the seller. The rest are set by the buyer’s own process and appear as limits the seller must meet. Confusing the two turns a shipment into a dispute.
| Specification line | What it measures | Where the number comes from | How to read it |
|---|---|---|---|
| Flake size | Width of a typical flake, set by the crusher screen | The line — 10–15 mm on SUHUI’s PET bottle sorting washing line | Consistency beats the number. Oversize bridges in the feed throat; fines scorch |
| Residual moisture | Water held in and on the flake after drying | The line — below 1% after thermal drying | A shipping figure, not a processing figure. The extruder needs far lower |
| Colour stream | Which optical sorting fraction the lot came from | The line — clear, light blue, or green | Caps the end market before anything else, and cannot be undone later |
| PVC content | Parts per million of PVC left among the flakes | The buyer’s contract; the line must stay under it | The most damaging contaminant. PVC decomposes at PET processing temperatures, causing yellowing and black specks |
| Metal content | Ferrous and non-ferrous fragments, mostly aluminium caps and foil | The buyer’s contract; a magnetic drum and eddy current separator remove it | Metal wrecks screen changers and melt filters, so the tolerance is rarely negotiable |
| Intrinsic viscosity (IV) | A proxy for polymer chain length, and so for melt strength | The buyer’s contract, matched to the end application | Washing and reprocessing pull IV down. A higher target needs solid state polymerization |
| Yellowness index | Drift from neutral toward yellow, reported as a b* value | The buyer’s contract, measured on their own colorimeter | A symptom of thermal and oxidative history, not something washing removes |
Notice how many cells say “the buyer’s contract”. SUHUI does not publish universal ppm ceilings, IV values, or b* limits, because those are commercial terms rather than properties of the equipment, and they differ from one market to the next.
Seven specification lines, split between what the recycling line produces and what the buyer’s contract demands.
How PET Flakes Are Made and Which Stage Sets Which Number
PET flakes are made by breaking bales, removing metals and non-PET bottles, stripping labels, crushing, hot washing, separating by density, drying, and optically sorting by colour. What matters for the specification is that each stage locks in a different line on the sheet, and once a stage passes, its number cannot be improved later.
| Stage on the line | What happens to the material | The specification line it locks in |
|---|---|---|
| Bale breaking and trommel screening | Bales are opened; loose dirt and debris fall out | Sets the ceiling on every purity figure that follows |
| Magnetic drum and eddy current separation | Ferrous metal is pulled out, then aluminium caps and foil | Metal content |
| Bottle-level optical sorting | PVC bottles, non-PET plastics, and heavily coloured bottles are ejected before crushing | PVC content — the cheapest point to remove it |
| Label removal and crushing | Sleeve and foil labels are stripped, then bottles are crushed and granulated | Flake size, at 10–15 mm |
| Pre-wash, dual hot alkaline wash, friction wash | Ambient rinse, then high-speed and low-speed hot washers at 80–90°C with alkaline solution, then friction scrubbing | Glue, oil, and organic residue — the gap between washed and hot washed PET flakes |
| Float-sink and zig-zag air separation | PET sinks while PP and PE caps and film float off; an air column lifts residual film | Polyolefin contamination |
| Centrifugal dewatering and thermal drying | Surface water is spun off, then hot air drying finishes | Residual moisture, to below 1% |
| Flake-level optical colour sorting | Flakes are split into clear, light blue, and green; opaque pieces ejected | Colour stream |
| Pelletizing and SSP (optional, downstream) | Flakes are melted, filtered, degassed, and cut; SSP extends chain length under nitrogen | Intrinsic viscosity |
Read that table as a diagnostic tool. A lot failing on PVC cannot be rescued by more washing, because PVC was supposed to leave at the optical sorter six stages earlier. Stage detail and capacities from 500 to 3,000 kg/h are on the PET bottle sorting washing line page.
Each stage locks in a different specification line, and a number missed at one stage cannot be recovered later.
The Two Moisture Numbers People Confuse
PET flakes carry two different moisture figures and they sit roughly fifty times apart. Below 1% is what a washing line delivers after thermal drying, and it is the number written on the shipping specification. Below 0.02% is what PET must reach before it enters an extruder. Treating the first as the second destroys material.
PET is hygroscopic and degrades by hydrolysis at melt temperature. Water present when the polymer melts cuts the chains, which shows up as falling intrinsic viscosity, weaker parts, and surface defects. That is why a compounding line such as the PET flakes twin screw pelletizing line puts washed PET flakes through a dehumidifying dryer to below 0.02% before compounding, then vents the barrel under vacuum.
The seller’s obligation ends at below 1%. Drying to 0.02% belongs to the converter and happens immediately before processing, because PET reabsorbs moisture from the air: a batch dried yesterday is not dry today.
Below 1% is a shipping figure. Below 0.02% is a processing figure, and the two sit roughly fifty times apart.
PET Flakes Compared With Chips, Regrind and Pellets
Flakes, regrind, pellets, and chips are four different materials that get quoted as if they were interchangeable. The distinctions that matter are whether the material has been melted and whether it has been washed. Melting adds a heat history and costs intrinsic viscosity; washing decides whether contamination was ever removed.
| Material | How it is produced | Typical form | What it means for the buyer |
|---|---|---|---|
| PET flakes | Bottles sorted, crushed, washed, dried, colour sorted — never melted | Irregular pieces around 10–15 mm | One heat history less than pellets, but needs drying and filtration at the converter |
| PET regrind | Production scrap ground dry, typically with no wash stage | Irregular, often with fines | Can be very clean if the scrap was, but carries no washing guarantee |
| rPET pellets | Washed flakes melted, filtered, vacuum degassed, strand cut | Uniform cylinders, 2–5 mm on a SUHUI strand pelletizer | Predictable feeding and melting, at the cost of one extra thermal cycle |
| PET chips | Varies by region — usually melt-produced granules, but some traders mean washed flakes | Depends which meaning is intended | Never accept “chips” on a contract without asking which process produced them |
Washed or not, melted or not. Those two questions separate four materials that are often quoted interchangeably.
What Clean PET Flakes Are Used For
Clean PET flakes go mainly into polyester fibre, sheet and thermoformed packaging, strapping, and pelletizing feedstock, with food-contact bottle-to-bottle recycling at the top of the value range. Which of those a lot can reach is decided by wash grade, and each grade has one specification line that governs acceptance.
| Flake grade | What the wash line has to do | The line that decides acceptance | Typical outlet |
|---|---|---|---|
| Washed flake | Pre-wash and rinse, basic separation, drying | Flake size and moisture | Lower-grade fibre, fillers, non-critical mouldings |
| Hot washed flake | Adds dual hot alkaline washing at 80–90°C plus friction scrubbing | Glue, oil, and polyolefin residue | Staple fibre, strapping, sheet |
| Clean sorted flake | Adds flake-level optical colour sorting | Colour stream and PVC content | Clear sheet, premium fibre, resale to converters |
| Food-contact grade | Adds validated downstream decontamination and traceability | The full specification, including IV and the buyer’s ppm limits | Bottle-to-bottle, subject to FDA and EU food-contact approval |
Recycled PET flakes aimed at the higher grades often need intrinsic viscosity restored first. That is the job of a PET solid state polymerization system, which extends the polymer chains below the melting point under circulating nitrogen while stripping out moisture, acetaldehyde, and ethylene glycol. How much IV it recovers depends on the starting material, temperature, and residence time, so the reactor is configured against the target application rather than sold with a fixed uplift figure. Where converting flakes to pellets in-house pays better than selling them, that route runs through the pelletizing line range.
Wash grade caps the end market. Each grade has one specification line that governs acceptance.
How to Check a Lot of PET Flakes Before You Accept It
Incoming inspection takes about twenty minutes per lot with basic equipment, and it catches the failures that are expensive to find at the extruder. The principle is straightforward: sample properly, separate what should not be there, weigh it, and keep a retained sample so any dispute has physical evidence behind it.
- Sample from depth, not from the top. Fines and light contaminants migrate during transport. Draw from several depths in each bulk bag, and from more than one bag.
- Hand-sort a weighed sample. Weigh a known quantity, pick out everything that is not PET flake, and weigh the rejects. That gives a contamination figure in minutes.
- Run a water float test. PET sinks; PP and PE float. A bucket reproduces the float-sink stage well enough to reveal cap and label film carryover.
- Measure moisture on arrival, then again before processing. Below 1% is the shipping expectation; below 0.02% is what your extruder needs, and your own dryer has to deliver it.
- Send for IV testing if the contract has an IV clause. Intrinsic viscosity cannot be judged by eye, and it is the clause most often argued over after the material is consumed.
- Retain a sealed sample from every lot, labelled with lot number and arrival date. Without one, a dispute becomes one party’s word against the other’s.
The Association of Plastic Recyclers publishes industry guidance on how recovered PET is evaluated, which is a useful reference when drafting or challenging an acceptance specification.
Twenty minutes of incoming inspection catches the failures that are expensive to find at the extruder.
Frequently Asked Questions
What is the difference between PET flakes and PET chips?
PET flakes are washed, crushed bottle material that has never been melted, typically 10–15 mm and irregular. PET chips usually means melt-produced granules, though some traders use it loosely for washed flakes. The two carry different heat histories, so confirm which process produced the material.
What are PET flakes used for?
Clean PET flakes go mainly into polyester staple fibre and filament, thermoformed sheet and packaging, PET strapping, and pelletizing feedstock. With validated decontamination and food-contact approval, high-purity flakes also serve bottle-to-bottle recycling, the highest-value outlet.
What chemical is used to wash PET flakes?
Industrial PET washing uses a hot alkaline solution, typically caustic soda with a detergent additive, at 80–90°C. The alkali saponifies oils and dissolves label adhesives that cold water leaves behind. On SUHUI’s PET bottle sorting washing line, chemical consumption runs from 10 to 28 kg/h across the 500–3,000 kg/h range.
What are the downsides of PET plastic in recycling?
Three properties make PET demanding. It is hygroscopic, so it must be dried below 0.02% before melting or it degrades by hydrolysis. Its intrinsic viscosity falls with each thermal cycle. And it is intolerant of PVC, which decomposes at PET processing temperatures and causes yellowing and black specks.
Where can PET flakes be sold?
The main buyers are polyester fibre producers, sheet and strapping extruders, compounders, and traders supplying them. Which will take a lot depends on its colour stream and wash grade. Clear hot washed flake has the widest market; mixed-colour flake is limited to lower-value fibre and filler uses.
How dry do PET flakes need to be?
Two answers, roughly fifty times apart. Below 1% residual moisture is the shipping specification delivered by thermal drying on the washing line. Below 0.02% is what PET must reach in a dehumidifying dryer immediately before extrusion, because the material reabsorbs atmospheric moisture in storage.
Before You Sign Off on a PET Flake Contract
PET flakes are a specification-traded commodity, and most of the risk sits in the gap between what the recycling line controls and what the contract demands. Flake size, moisture, and colour stream come from the line. PVC and metal limits, IV targets, and yellowness ceilings come from the buyer.
If you are producing flakes, work backwards from the specification you have to meet and check that your line has a stage responsible for every line on it. If you are buying, inspect on arrival and retain a sample. To review a project from either side, contact SUHUI Machinery with your bale source and target capacity.
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