Single screw extruders are common in plastics processing, and they can also pelletize PET bottle flakes into rPET pellets\u2014if<\/em> the line controls moisture, volatiles, filtration, and pelletizing well enough to protect intrinsic viscosity (IV) and pellet quality.<\/p>\n 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.<\/p>\n For a baseline configuration and options, see Energycle\u2019s PET flake single screw pelletizer reference page<\/a>.<\/p>\n If you\u2019re still scoping equipment, these Energycle pages help you compare line concepts and terminology: – plastic pelletizer machines<\/a> – pelletizing methods in plastic pelletizers<\/a> – plastic recycling machines overview<\/a><\/p>\n 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)<\/a>)<\/p>\n That\u2019s the core reason PET pelletizing lines look \u201cover-equipped\u201d compared with PP\/PE: PET punishes weak drying control, long residence time, and unstable venting.<\/p>\n Most buyers say \u201cpelletizer,\u201d but the system is a line made of multiple modules: – Feed prep<\/strong> (buffering, metal detection, optional densification) – Drying \/ pre-drying<\/strong> (often the most important module for PET) – Extrusion<\/strong> (single screw, commonly with venting and vacuum) – Melt filtration<\/strong> (screen changer<\/a> or continuous filtration, sometimes with a melt pump) – Pelletizing + pellet handling<\/strong> (strand or underwater; then drying and fines removal)<\/p>\n 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.<\/p>\n Most lines follow a flow similar to this:<\/p>\n 1) Washed PET flakes (with controlled PVC\/metal\/paper limits) Some \u201cbottle-to-bottle\u201d processes add additional decontamination and IV management steps (for example, EREMA\u2019s 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<\/a>).<\/p>\n 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).<\/p>\n Buyer checks: – How is moisture measured (sampling point and method)? – What moisture range can the supplier guarantee at extruder feed on your<\/em> flakes? – What happens during start\/stop events and hopper refills (moisture spikes are common)?<\/p>\n 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<\/a>.)<\/p>\n PET flakes can bridge, surge, or carry fines into the extruder. A stable feed improves melt pressure stability and makes filtration easier to manage.<\/p>\n Buyer checks: – Hopper design and anti-bridging features – How the supplier deals with light labels\/fines – Whether densification\/compaction is used (and why)<\/p>\n Degassing is where many lines gain stability. It helps remove water vapor and other volatiles from the melt\u2014especially important for rPET with variable incoming quality.<\/p>\n Two practical things to verify: – Carryover control<\/strong> (how the vent prevents melt from being pulled into the vacuum line) – Vacuum system durability<\/strong> (because PET degassing can pull vapors such as water, solvents, monomers\/oligomers, plus entrained particles into the system)<\/p>\n Leybold\u2019s 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<\/a>.)<\/p>\n 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.<\/p>\n What good looks like: – Pressure is stable enough to keep pellet size consistent – Filter maintenance fits your campaign length (not your worst hour)<\/p>\n Gneuss highlights a common operational issue\u2014screen changes causing interruptions and pressure spikes\u2014and describes a rotary filtration concept aimed at keeping melt flow conditions (including pressure drop) constant by controlling screen contamination. (See Gneuss melt filtration overview<\/a>.)<\/p>\n Starlinger\u2019s 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<\/a>.)<\/p>\n Pelletizing is not only \u201ccutting.\u201d It\u2019s also water\/air handling, pellet drying, fines control, and how tolerant the line is to small melt variations.<\/p>\n Underwater pelletizing systems are often specified as complete packages because multiple subsystems must match. Plastics Technology notes that an underwater pelletizer \u201ccan only be successful with the proper specification of extruders, pumps, filters, water systems and dryers coordinated to achieve consistent pellet quality.\u201d (See Plastics Technology on underwater pelletizing system specification<\/a>.)<\/p>\n If you are deciding between pelletizing methods, ask suppliers to show pellet quality (fines %, tails, pellet size distribution) at your target throughput and IV\u2014not only at a \u201chappy path\u201d condition. For a practical breakdown of common options, see Energycle\u2019s guide to pelletizing methods in plastic pelletizers<\/a>.<\/p>\nQuick Takeaways (For Buyers)<\/h2>\n
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Why PET Flake Pelletizing Is Sensitive: Moisture \u2192 Hydrolysis \u2192 IV Loss<\/h2>\n
What \u201cSingle Screw Pelletizer for PET Flakes\u201d Actually Means<\/h2>\n
Typical Process Flow (Bottle Flakes \u2192 rPET Pellets)<\/h2>\n
\n2) Pre-drying \/ dryer buffer (target moisture stability)
\n3) Feeding system (hopper design, bridging control, optional densifier\/compactor)
\n4) Single screw extruder (temperature profile + residence time control)
\n5) Vacuum degassing\/venting (remove water vapor and other volatiles)
\n6) Melt filtration (remove solid contaminants; control pressure stability)
\n7) Pelletizing (strand or underwater)
\n8) Pellet drying + fines removal + conveying to storage<\/p>\nCore Modules (What to Inspect and What It Changes)<\/h2>\n
1) Drying \/ Pre-Drying (Often the Highest ROI Upgrade)<\/h3>\n
2) Feeding and Flake Handling (Stability Beats Peak Output)<\/h3>\n
3) Vacuum Degassing \/ Venting (Moisture + Volatiles Control)<\/h3>\n
4) Melt Filtration + Pressure Stability (The \u201cQuiet Line\u201d Advantage)<\/h3>\n
5) Pelletizing Method (Strand vs Underwater) and Pellet Handling<\/h3>\n
Single Screw vs Twin Screw for PET Flakes (Buyer Decision Table)<\/h2>\n