Processing 100% recycled PET bottle flakes (rPET) into high-clarity, thermoforming-grade sheet reels is one of the most profitable and sustainable choices in modern plastic packaging. However, rPET presents unique processing challenges—primarily moisture sensitivity, intrinsic viscosity (IV) degradation, and impurities.
To produce clear, durable PET sheets efficiently without excessive energy costs, manufacturers rely on modern extrusion technology such as parallel twin-screw extruders and ABA three-layer co-extrusion systems.
Key Challenges in Processing Recycled PET Flakes
Before looking at machine configurations, it is critical to understand what happens when processing post-consumer PET bottle flakes:
- Hydrolysis & IV Loss: PET is hygroscopic. Moisture at high melt temperatures causes hydrolysis, breaking polymer chains and dropping intrinsic viscosity (IV), resulting in brittle sheets.
- Impurity Inconsistencies: Recycled flakes often contain residual PVC, polyolefins (caps/labels), or moisture variations.
- Yellowing and Clarity Loss: Thermal degradation during prolonged heat exposure leads to optical defects and discoloration.
Step-by-Step Process: From Flakes to Finished Sheet Reels
Step 1: Flake Preparation & Dosing
Post-consumer bottle flakes are washed, metal-separated, and sorted by color. Multi-component gravimetric dosing units ensure precise feeding of rPET flakes, virgin PET chips, or masterbatch additives.
Step 2: Extrusion & Devolatilization (Drying vs. Non-Drying)
Traditionally, PET required 4–6 hours of energy-intensive pre-drying and crystallization. Modern extrusion equipment bypasses this step.
Parallel Twin Screw PET Sheet Extrusion Machine (Non-Drying Technology): Equipped with high-vacuum multi-stage degasification (vacuum systems down to < 5 mbar), parallel twin-screw extruders continuously extract moisture and volatiles directly from the melt. This prevents hydrolysis without requiring separate pre-drying equipment, significantly lowering energy consumption.
Step 3: Melt Filtration & Gear Pump Metering
Because recycled bottle flakes carry microscopic contaminants, high-area continuous screen changers (backflush or hydraulic piston style) filter out particulate matter. A high-precision melt pump then maintains stable, pulse-free pressure into the T-die.
Step 4: Co-Extrusion & Layer Structuring (ABA Structure)
To optimize material costs while maintaining superior surface properties, packaging manufacturers utilize co-extrusion.
ABA PET Three-Layer Sheet Co-Extrusion Lines:
- A Layers (Outer Surfaces, ~10-20% each): Virgin PET or high-grade anti-block/virgin blend to ensure excellent clarity, printability, and food-contact compliance.
- B Layer (Core Layer, ~60-80%): 100% recycled PET flakes (rPET) or internal skeleton scrap.
This structure allows manufacturers to maximize rPET usage in the core while securing crisp, food-safe, and thermoforming-ready outer surfaces.
Step 5: Calendering, Cooling & Winding
The molten sheet exits the T-die into a 3-roll calendar unit for precise thickness control, cooling, and surface finishing (gloss or matte). The cooled sheet is continuously trimmed, scanned for thickness accuracy, and wound into tight rolls.
Comparing Machinery Solutions for PET Flake Processing
| Extrusion Feature | Single Screw (Traditional) | Parallel Twin Screw | ABA Three-Layer Co-Extrusion |
|---|---|---|---|
| rPET Flake Ratio | 20% – 50% max | Up to 100% | Up to 100% core layer |
| Requisito de pré-secagem | Mandatory (Dehumidifying) | Not required (High Vacuum) | Depends on extruder selection |
| Consumo de energia | Higher (pre-heating needed) | 30-40% lower | Optimized per layer |
| Melt Homogeneity | Moderado | Exceptional shear & mixing | Ideal for multi-material cost efficiency |
| Vantagem principal | Lower capital cost | Direct flake processing | Premium surface + high rPET core |
Why TZ Machinery Equipment Leads in PET Sheet Extrusion
When selecting an extrusion system for recycled PET bottle flakes, process stability and energy efficiency are paramount. TZ Machinery offers specialized technical configurations designed specifically for high-flake conversion:
- Parallel Twin Screw PET Sheet Extrusion Machine: Designed with modular co-rotating twin screws that deliver superior dispersion, self-wiping melt action, and deep vacuum degasification for direct rPET processing without pre-drying.
- ABA PET Three-Layer Sheet Co-Extrusion Lines: Engineered for maximum profitability, allowing factories to run lower-cost recycled flakes in the center core while maintaining crystal-clear outer layers for food containers, blister packs, and thermoformed products.
Perguntas frequentes
Can you make PET sheet using 100% recycled bottle flakes?
Yes. Using a parallel twin-screw PET sheet extrusion line with high-vacuum devolatilization, 100% post-consumer recycled PET flakes can be processed directly into thermoforming-grade sheet reels without prior crystallization or dehumidification drying.
What is the advantage of an ABA structure in PET sheet co-extrusion?
An ABA three-layer structure allows manufacturers to put recycled PET flakes or factory trim regrind in the center core (B layer) while placing virgin PET or functional additives on the outer skins (A layers). This reduces raw material costs while keeping surface appearance and food-contact safety intact.
Why is vacuum degassing necessary for PET flake extrusion?
PET rapidly degrades in the presence of heat and moisture (hydrolysis). Multi-stage high-vacuum degassing removes water vapor and volatile impurities directly from the polymer melt during twin-screw extrusion, preserving the intrinsic viscosity (IV) of the material.