Material
Recycled PET Flakes
Answer in brief
Flakes are not pellets, and equipment sized for pellets will disappoint.
They are flat, irregular and light, so they interlock in hoppers, cling to walls with static and take far more volume per tonne than virgin resin.
- Expect bridging and design the outlet accordingly.
- Dry before extrusion, because PET hydrolyses at melt temperature.
- Remove metal and foreign flake before the material reaches a feeder.
Reviewed October 21, 2026 · Updated October 21, 2026
Handling challenges
Recycled PET arrives as a flake with a shape that nobody designed for conveying.
The particle is thin, curved and variable, which means the bulk behaves by interlocking rather than by the friction rules that work for granules.
Bridging and hopper design
- Outlet size driven by flake length, not by equivalent particle diameter.
- Steep walls and smooth liners, since a shallow cone simply holds the arch.
- Live bottom or agitated discharge where the silo is tall and consolidation is real.
A bridge in flake material often looks stable enough to walk on, which makes silo entry one of the more dangerous tasks in a recycling plant.
Static and light weight
Dry flake generates and holds static, so it clings to sight glasses, filter bags and conveying line walls.
Grounding is necessary but will not fix the clinging; controlled conveying velocity and attention to line layout do more.
Moisture and drying
PET hydrolyses in the extruder if moisture is present, and the result is low intrinsic viscosity and a weak product.
Drying to the required dew point and protecting the dried material from re-absorption between dryer and extruder are part of the handling design, not a separate process step.
Contamination control
Label fragments, adhesives, aluminium and foreign polymers all survive washing to some degree.
Metal detection, air classification and inline screening before the feeder protect both the extruder screw and the food-grade claim of the pellet.
What to establish before buying equipment
- Flake size distribution including the longest particles, which set the outlet.
- Bulk density range, which is lower and more variable than for pellets.
- Required dryness at the extruder inlet.
- Acceptance limits for foreign material and the detection method.
Material behavior
- Flowability
- Poor; flakes interlock and bridge
- Abrasiveness
- Low to moderate
- Cohesiveness
- Mechanical interlocking rather than true cohesion
- Moisture behavior
- Must be dried before extrusion to avoid chain degradation
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