Pelletizing is the step where washed flakes or film become a sellable product: uniform, clean plastic pellets that compounders and manufacturers can feed straight into their own extruders. The extruder you choose — single-screw, two-stage single-screw, or twin-screw — decides your pellet quality, your stable throughput, and a large share of your operating cost. This guide explains how a pelletizing line works and matches each common material to the right line configuration.
How a Plastic Pelletizing Line Works
A complete pelletizing line turns loose flakes or film into pellets in five stages. First, the feed system meters material into the extruder at a steady rate — a compactor or densifier pre-compresses light, fluffy film so it feeds evenly instead of bridging. Second, the extruder melts and homogenizes the plastic. Third, melt filtration removes gels, paper fibers, and fine contaminants through screen changers or laser filters. Fourth, vacuum degassing pulls out moisture and volatile gases that would otherwise cause bubbles or odor in the pellets. Finally, the melt is cut into pellets — by water-ring, strand, or underwater pelletizing — then dried, cooled, and packed.
Pelletizing almost always follows washing and drying. If flakes enter the extruder wet, steam forms inside the melt and pellet quality collapses, so a centrifugal dryer or thermal dryer upstream is part of getting this stage right.
Single-Screw, Two-Stage, or Twin-Screw: Which Extruder for Pelletizing?
The three common extruder configurations for plastic recycling each suit different feeds:
- Single-screw extruder. Simple, robust, and cost-effective. Best for clean, uniform melts such as washed rigid flakes with low contamination. Limited mixing and degassing capacity compared with the other two.
- Two-stage single-screw extruder. Adds a second screw stage with extra vacuum venting and filtration between stages. The workhorse for washed PP/PE films, bags, and woven-bag regrind — it stabilizes volatile removal and filters fines from thin films at modest capital cost. A densifier or compactor ahead of it keeps light film feeding steadily.
- Twin-screw extruder (co-rotating). Intermeshing screws give far stronger mixing, dispersion, and degassing, with independent control of throughput and screw speed. The right choice for masterbatch and high-filler compounds, elastomers like TPU/TPV, PVC regrind, and PET flakes where moisture and viscosity (IV) must be tightly controlled.
As a rule of thumb: the dirtier, lighter, or more complex your feed, the more the line leans toward two-stage or twin-screw. Clean and simple melts run well on a single-screw.
Three Details That Decide Pellet Quality
1. Degassing. Vacuum vents along the barrel pull moisture and volatiles out of the melt. Double vacuum zones — standard on two-stage lines — make a visible difference on films and washed flakes that carry residual dampness. Poor degassing shows up as bubbles, splay marks, or odor in the finished pellets.
2. Filtration. Screen changers with large filtration area catch gels and fine contaminants before they reach the die. For tougher feeds, a laser filter system continuously ejects contaminants without stopping production — you can see one running on a PP/HDPE line in the videos below.
3. Pelletizing method. Water-ring pelletizers suit most commodity recycling (PP, PE, HDPE) and produce glossy, uniform pellets. Strand pelletizing with a water bath and air knife is simple and reliable for rigid-flake lines. Underwater (die-face) pelletizing cuts sticky melts cleanly — the standard choice for elastomers and soft compounds.
Which Pelletizing Line Fits Your Material?
Quick selector. “Why this choice” reflects how each configuration behaves in real recycling plants: single-screws are simpler and cost-effective for clean, simple melts; twin-screws deliver superior mixing and degassing for complex recipes and unstable feeds.
| Material / Feed | Recommended Line | Core options | Why this choice |
| Clean PP/PE films & bags (washed, low ash) | Two-stage single-screw (with densifier/compactor + water-ring) | Double vacuum vents; double filtration; VFD dosing; water-ring pelletizer | Two-stage stabilizes volatile removal and filters fines from thin films for consistent pellets at modest CAPEX. |
| Washed rigid HDPE/PP flakes (crates, caps) | Two-stage single-screw (strand or water-ring) | Side feeder; melt pump; strand bath + air knife or water-ring | Rigid flakes run well on single-screw if clean and dry; two-stage improves stability when fines or moisture vary. |
| PET flakes | Twin-screw (with dual-zone vacuum) or specialized single-screw with deep vacuum; strand or underwater | Dual vacuum; fine filtration; IV control strategy | PET is sensitive to moisture and IV; robust degassing and tight temperature control are mandatory for stable pellet quality. |
| Woven bags / film regrind (medium contamination) | Two-stage single-screw (compactor + double vent) | Double filtration; large screen area; water-ring | Extra filtration and venting smooth out gels and volatiles; the compactor gives steady feed for light, fluffy films. |
| Masterbatch / high-filler compounds (CaCO3, glass fiber, additives) | Co-rotating twin-screw (side feeders + modular kneading blocks) | Melt pump; side-feed solids/liquids; water-ring/underwater | The intermeshing design gives stronger mixing and dispersion, with independent control of throughput vs. screw speed. |
| Elastomers / TPU / TPV | Co-rotating twin-screw + underwater pelletizing | Tight temp windows; underwater die-face | Underwater cutting handles sticky melts cleanly; twin-screw controls shear and temperature precisely for uniform pellets. |
| PVC regrind | Twin-screw (counter or co-rotating) with de-HCl strategy | Venting; corrosion-resistant metallurgy; die-face cutting + air cooling | PVC needs strong venting and a gentle thermal profile; twin-screw hardware and configurations address both. |
Video Demonstrations
PP/HDPE Pelletizing Line with Laser Filter System
Watch how a laser filter system keeps pellets clean even with tough contaminants.
PP, PE and HDPE Regrind Pelletizing Line (Charlotte, USA)
PP, PE, and HDPE flakes turned into uniform pellets.
BOPP Plastic Film Pelletizing Line (Halifax, UK)
BOPP film waste recycled into new pellets, full process.
PP/PE Plastic Film Pelletizing Line (Auburn, USA)
Two-stage line processing PP/PE films with stable feeding and glossy pellets.
PET Flakes Pelletizing Line (Malaysia)
Twin-screw line processing PET bottle flakes.
Why Choose ASG
- One-stop solution: From films and woven bags to PET flakes, masterbatch, and PVC — one supplier covers the full range.
- Stable and efficient: Every line is built for real recycling conditions, with reliable degassing, steady feeding, and efficient pelletizing.
- Customizable: Capacity from 50 kg/h to 1,500 kg/h. Water-ring, strand, or underwater pelletizing — matched to your product.
- Trusted worldwide: Lines running in more than 60 countries, helping recyclers and compounders turn waste into value.
Frequently Asked Questions
What is the difference between single-screw and twin-screw pelletizing?
A single-screw extruder is simpler and cheaper, and works well for clean, uniform melts like washed rigid flakes. A co-rotating twin-screw gives much stronger mixing, dispersion, and degassing, which matters for masterbatch, filled compounds, elastomers, PVC, and PET — materials where recipe uniformity or moisture control decides pellet quality.
Why choose a two-stage single-screw line for film?
Thin films carry fines, labels, and residual moisture that make a single venting stage struggle. The second stage adds another vacuum zone and another filtration step, which stabilizes degassing and removes fine contaminants — giving consistent pellets from washed PP/PE films, bags, and woven-bag regrind at a moderate equipment cost.
What does vacuum degassing do in pelletizing?
Vacuum vents pull moisture and volatile gases out of the melt before it reaches the die. Without effective degassing, pellets come out with bubbles, surface defects, or odor — and downstream extrusion becomes unstable. Double vacuum zones are standard on lines built for film and washed flakes.
Water-ring, strand, or underwater pelletizing — which should I pick?
Water-ring suits most commodity recycling (PP, PE, HDPE) and makes glossy, uniform pellets. Strand pelletizing through a water bath is simple and dependable for rigid-flake lines. Underwater (die-face) cutting is the standard for sticky melts like TPU, TPV, and elastomers, where strands would clump.
How clean must my material be before pelletizing?
It depends on the line. Washed film and flakes from a proper film washing line or PET bottle washing line are the normal feed. Heavier contamination needs stronger filtration (larger screen area or a laser filter) and more venting — tell your supplier the real contamination level so the line is configured for it, not for ideal material.
What capacity range do pelletizing lines cover?
ASG pelletizing lines are built from 50 kg/h for small or specialized operations up to 1,500 kg/h for industrial recycling plants. The right size depends on your available feedstock volume, operating hours, and how the line balances with your upstream washing and drying capacity.
Can one line handle both film and rigid flakes?
A two-stage single-screw line with a compactor can handle both, but changeovers take time and die/pelletizer settings differ. Plants that run both materials regularly often dedicate the line to one family and size it for their main feed, or add quick-change filtration to cut changeover downtime.
What is a laser filter, and when is it worth it?
A laser filter uses a rotating scraper over a laser-drilled screen to eject contaminants continuously without stopping the line for screen changes. It pays off on feeds with persistent fine contamination — printed film, agricultural film, or woven bags — where conventional screen changers would need constant attention.
How do I get a tailored proposal?
Tell us three things: what material you process, how clean it is, and your target output in kg/h. With that we can recommend the extruder configuration, filtration, and pelletizing method, and send a proposal with capacity, specs, and pricing. Use the form below or visit our contact page.
Your Next Step
Not sure which line fits your material? Tell us:
- What material you process
- How clean it is
- Your target output (kg/h)
We’ll send you a tailored proposal with capacity, specs, and pricing — clear and fast.
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