Single screw extruders are common in plastics processing, and they can also pelletize PET bottle flakes into rPET pellets—si the line controls moisture, volatiles, filtration, and pelletizing well enough to protect intrinsic viscosity (IV) and pellet quality.
This guide explains what a single screw PET flake pelletizer is, how the full line is typically configured, where projects fail, and what to ask suppliers before you sign a purchase order.
For a baseline configuration and options, see Energycle’s PET flake single screw pelletizer reference page.
If you’re still scoping equipment, these Energycle pages help you compare line concepts and terminology:
– machines de granulation de plastique
– pelletizing methods in plastic pelletizers
– plastic recycling machines overview
Quick Takeaways (For Buyers)
- PET flakes must be dried to very low moisture before melting; moisture in the melt can drive hydrolysis and IV loss.
- Vacuum degassing and stable melt filtration are often the difference between “runs” and “runs consistently.”
- Single screw lines are frequently used for many rPET pellet applications, while twin screw becomes more attractive as mixing/compounding needs rise.
Why PET Flake Pelletizing Is Sensitive: Moisture → Hydrolysis → IV Loss
PET readily absorbs moisture. When PET is melted with moisture present, hydrolysis can occur and reduce molecular weight, which shows up as IV loss and reduced mechanical performance. A recycling industry guidance document on PET handling and drying notes that even small moisture levels can hydrolyze PET during melt processing and that PET must be thoroughly dried immediately before melt processing to minimize IV loss. It also gives commonly cited targets such as drying to ~50 ppm moisture and keeping IV loss within a narrow band for typical recycled PET applications. (Source: CWC PET drying guidance (BP-PET3-05-01))
That’s the core reason PET pelletizing lines look “over-equipped” compared with PP/PE: PET punishes weak drying control, long residence time, and unstable venting.
What “Single Screw Pelletizer for PET Flakes” Actually Means
Most buyers say “pelletizer,” but the system is a line made of multiple modules:
– Feed prep (buffering, metal detection, optional densification)
– Drying / pre-drying (often the most important module for PET)
– Extrusion (single screw, commonly with venting and vacuum)
– Melt filtration (screen changer or continuous filtration, sometimes with a melt pump)
– Pelletizing + pellet handling (strand or underwater; then drying and fines removal)
When you compare suppliers, focus less on the screw alone and more on how the modules work together to control IV, contamination, and pellet consistency.
Typical Process Flow (Bottle Flakes → rPET Pellets)
Most lines follow a flow similar to this:
1) Washed PET flakes (with controlled PVC/metal/paper limits)
2) Pre-drying / dryer buffer (target moisture stability)
3) Feeding system (hopper design, bridging control, optional densifier/compactor)
4) Single screw extruder (temperature profile + residence time control)
5) Vacuum degassing/venting (remove water vapor and other volatiles)
6) Melt filtration (remove solid contaminants; control pressure stability)
7) Pelletizing (strand or underwater)
8) Pellet drying + fines removal + conveying to storage
Some “bottle-to-bottle” processes add additional decontamination and IV management steps (for example, EREMA’s VACUREMA describes defined vacuum treatment and solid-phase polycondensation/IV increase steps as part of its concept, and notes that melting under vacuum helps prevent hydrolytic/oxidative decomposition; see EREMA VACUREMA details).
Core Modules (What to Inspect and What It Changes)
1) Drying / Pre-Drying (Often the Highest ROI Upgrade)
If your dryer cannot hold stable moisture at the extruder feed, you will chase problems downstream (foaming, bubbles, haze, pellet inconsistency, frequent reversals of settings).
Buyer checks:
– How is moisture measured (sampling point and method)?
– What moisture range can the supplier guarantee at extruder feed on ton flakes?
– What happens during start/stop events and hopper refills (moisture spikes are common)?
If you need a target to discuss with suppliers, the CWC PET drying guidance notes drying to very low moisture levels (commonly referenced around tens of ppm) to minimize hydrolysis during melt processing. (See CWC PET drying guidance.)
2) Feeding and Flake Handling (Stability Beats Peak Output)
PET flakes can bridge, surge, or carry fines into the extruder. A stable feed improves melt pressure stability and makes filtration easier to manage.
Buyer checks:
– Hopper design and anti-bridging features
– How the supplier deals with light labels/fines
– Whether densification/compaction is used (and why)
3) Vacuum Degassing / Venting (Moisture + Volatiles Control)
Degassing is where many lines gain stability. It helps remove water vapor and other volatiles from the melt—especially important for rPET with variable incoming quality.
Two practical things to verify:
– Carryover control (how the vent prevents melt from being pulled into the vacuum line)
– Vacuum system durability (because PET degassing can pull vapors such as water, solvents, monomers/oligomers, plus entrained particles into the system)
Leybold’s extruder degassing overview describes PET degassing as extracting significant amounts of vapors (including water, solvents, monomers, oligomers) from the extruder into the vacuum system, and notes the design challenge of handling condensation and polymerization in pumps. (See Leybold extruder degassing overview.)
4) Melt Filtration + Pressure Stability (The “Quiet Line” Advantage)
Flake contamination is real: paper, aluminum, elastomers, occasional PVC, and fines. Your melt filter needs to remove solids without creating disruptive pressure spikes or frequent downtime.
What good looks like:
– Pressure is stable enough to keep pellet size consistent
– Filter maintenance fits your campaign length (not your worst hour)
Gneuss highlights a common operational issue—screen changes causing interruptions and pressure spikes—and describes a rotary filtration concept aimed at keeping melt flow conditions (including pressure drop) constant by controlling screen contamination. (See Gneuss melt filtration overview.)
Starlinger’s recoSTAR PET line description also emphasizes melt filtration and stable melt pressure, noting the role of a melt pump in stabilizing pressure and supporting consistent melt quality. (See Starlinger recoSTAR PET overview.)
5) Pelletizing Method (Strand vs Underwater) and Pellet Handling
Pelletizing is not only “cutting.” It’s also water/air handling, pellet drying, fines control, and how tolerant the line is to small melt variations.
Underwater pelletizing systems are often specified as complete packages because multiple subsystems must match. Plastics Technology notes that an underwater pelletizer “can only be successful with the proper specification of extruders, pumps, filters, water systems and dryers coordinated to achieve consistent pellet quality.” (See Plastics Technology on underwater pelletizing system specification.)
If you are deciding between pelletizing methods, ask suppliers to show pellet quality (fines %, tails, pellet size distribution) at your target throughput and IV—not only at a “happy path” condition. For a practical breakdown of common options, see Energycle’s guide to pelletizing methods in plastic pelletizers.
Single Screw vs Twin Screw for PET Flakes (Buyer Decision Table)
| Decision factor | Single screw is often a fit when… | Twin screw is often a fit when… |
|---|---|---|
| Flake consistency | Incoming flakes are consistently washed and sorted | Incoming quality swings and you need more processing “headroom” |
| Mixing/compounding | You mainly need melting, degassing, filtration, and pelletizing | You need stronger mixing for additives, fillers, color, or controlled compounding |
| Devolatilization needs | One or two well-designed vent/vacuum zones can meet targets | You need more aggressive devolatilization capability and mixing |
| Maintenance model | You want fewer rotating elements and simpler rebuild routines | You accept more complex maintenance for the process flexibility |
| Risk tolerance | You can enforce tight input specs (moisture/contamination) | You need the process to tolerate wider input variability |
The fastest way to decide is to define your target pellet IV, contamination window, and end-market requirements, then confirm with a material trial using your flakes.
Specs You Should Define Before You Request a Quote
Many “wrong machine” purchases happen because the quote is built around throughput only. Use a spec sheet that includes quality, variability, and compliance needs.
| Spec item | Pourquoi c'est important | How to define it |
|---|---|---|
| Incoming flake moisture | Direct driver of hydrolysis risk and IV loss | Provide typical/worst-case moisture; define the measured feed moisture target at extruder inlet (cite your test method) |
| Incoming contamination profile | Determines filtration load and pellet defects | Define PVC limit, metals, paper/labels, fines %, and non-melting contaminants |
| Target pellet IV and IV loss limit | Defines mechanical performance and end-use | State IV target range and allowable IV loss; verify measurement method (ASTM D4603 is commonly referenced) |
| Odor/VOC expectations | Affects end-market acceptance | Define odor/VOC target and how it will be evaluated (customer panel, instrument, etc.) |
| Pellet geometry + fines limits | Affects conveying, dosing, and downstream quality | Define pellet size range and acceptable fines; include dryer and fines removal expectations |
| Food-contact intent (if applicable) | May require additional validation and documentation | Define end market and compliance path; review FDA’s guidance on recycled plastics for food packaging chemistry considerations |
FDA reference for teams targeting food-contact applications: Use of Recycled Plastics in Food Packaging (Chemistry Considerations): Guidance for Industry.
Supplier Questions That Save Projects
Ask these early, before the supplier locks a configuration:
1) Drying guarantee: What moisture at extruder feed do you guarantee on my flakes, and how do you measure it?
2) Degassing design: What prevents melt carryover into the vacuum line, and what is the maintenance plan for the vacuum system?
3) Filtration plan: What contamination load assumptions are you using, what fineness can you maintain, and what does a “bad day” look like for screen changes or backflushing?
4) Melt pressure stability: Do you use a melt pump, and what pressure fluctuation range do you expect at steady state?
5) Pellet quality proof: Show pellet size distribution and fines at my target throughput, and explain how the pellet dryer and fines removal are sized.
6) Trial protocol: What will we measure during the trial (IV, gels, black specs, VOC/odor), and what constitutes pass/fail?
For planning downtime and parts, Energycle’s plastic pelletizer maintenance checklist can help you turn “maintenance” into a real PM schedule.
FAQ (Real Procurement Questions)
Can a single screw line produce food-contact rPET pellets from bottle flakes?
It can, but “food-contact” is a compliance and process-control question, not only a screw choice. You need tight input control (sorting, washing, and low PVC/metal) plus a decontamination concept that your end market accepts. Some suppliers position complete bottle-to-bottle systems with defined vacuum treatment time and temperature; for example, EREMA describes minimum vacuum treatment time and higher-temperature treatment for PET flakes in its VACUREMA concept. For U.S. projects, also review the FDA guidance on recycled plastics for food packaging and align your validation plan with your customer’s requirements.
What moisture level should the supplier guarantee at the extruder feed throat?
Ask for a guaranteed range at the extruder inlet, not only “dryer performance.” PET is sensitive to moisture in the melt because hydrolysis can reduce molecular weight and IV. A PET recycling drying guidance document discusses drying PET to very low moisture (commonly referenced around tens of ppm) to minimize hydrolysis and limit IV loss during melt processing. Use that as a starting reference, then set a number based on your target IV and end use. Most importantly, specify the sampling point, test method, and how the supplier will handle moisture spikes during hopper refills and startups. (See CWC PET drying guidance.)
Which melt filtration approach is safer for post-consumer flakes: screen changer or continuous filtration?
The right choice depends on contamination load and uptime expectations. Screen changers can work well when contamination is controlled, but frequent screen changes can cause pressure swings and process interruptions if the line is not designed for them. Continuous filtration concepts aim to keep melt flow conditions steadier; for example, Gneuss describes filtration approaches that maintain constant conditions by controlling screen contamination, helping avoid pressure spikes associated with screen changes. When you compare offers, ask each supplier for the assumed contamination load, the expected maintenance interval at your throughput, and the data they use to predict pressure stability. (See Gneuss melt filtration overview.)
Do I need a melt pump on a PET pelletizing line?
A melt pump is not mandatory, but it can help when you need stable melt pressure at the die for consistent pellet size and steadier operation—especially if filtration causes variable pressure drop. Starlinger’s recoSTAR PET description highlights the melt pump’s role in stabilizing melt pressure and supporting consistent melt quality. For buyers, the decision comes down to: how tight your pellet size/fines limits are, how variable your incoming flakes are, and how stable you need the die pressure to be for your pelletizing method. Ask the supplier to show pressure trend data with and without the pump at your target filter fineness. (See Starlinger recoSTAR PET overview.)
What should I specify for vacuum degassing to avoid deposits and pump problems?
Start with what comes out of rPET melts: water vapor plus other vapors and sometimes entrained particles. Leybold notes that PET degassing can extract vapors such as water, solvents, monomers/oligomers, and that these can condense and polymerize inside vacuum pumps, creating a design and maintenance challenge. For procurement, ask what traps/condensers are included, how deposits are managed, what the cleaning interval is, and whether maintenance can align with your production campaigns. Also ask how the vent prevents melt carryover into the vacuum system during surges. (See Leybold extruder degassing overview.)
Strand pelletizing or underwater pelletizing—what reduces pellet defects and fines for PET?
Both can work; the deciding factor is system matching and operating window. Underwater systems can produce consistent pellets, but they require coordinated specification of upstream and downstream equipment. Plastics Technology notes that the underwater pelletizer’s success depends on proper specification of extruders, pumps, filters, water systems, and dryers to achieve consistent pellet quality. For PET buyers, request a pellet quality acceptance criteria list (fines %, tails, pellet size spread) and ask the supplier to run (or show) comparable data at your target IV and throughput. Also include dryer and fines removal in the quote; defects often show up after drying. (See Plastics Technology on underwater pelletizing system specification.)
Références
- Energycle — PET flake single screw pelletizer product reference: https://www.energycle.com/pet-plastic-flake-single-screw-pelletizer/
- CWC — PET recycling handling and processing: drying methods and requirements (BP-PET3-05-01): https://p2infohouse.org/ref/14/13537.pdf
- EREMA — VACUREMA technology details (vacuum treatment, melting under vacuum, filtration concepts): https://www.erema.com/en/vacurema_details/
- Leybold — Extruder degassing overview (PET vapors and vacuum system considerations): https://www.leybold.com/en/products/systems-and-solutions/customized-vacuum-systems/extruder-degassing
- Gneuss — Melt filtration overview (pressure stability and continuous filtration concepts): https://www.gneuss.com/en/trouble-free-melt-filtration/
- Starlinger — recoSTAR PET overview (melt filtration, melt pump, process features): https://www.starlinger.com/en/recycling-technology/recostar-pet
- FDA — Use of Recycled Plastics in Food Packaging (Chemistry Considerations): Guidance for Industry: https://www.fda.gov/media/150792/download
- ASTM — Intrinsic viscosity of PET (ASTM D4603 overview): https://store.astm.org/d4603-18.html
- ISO — Plastics recycling guideline (ISO 15270 overview): https://www.iso.org/standard/15270.html
