Pet Bottle Flakes Pelletizing Machine

Compared to manufactured flakes, pellets offer the following advantages

Superior plasticizing effect with consistent output quality

The screw design offers excellent shearing and mixing performance, ensuring a uniform PET melt and stable IV (Intrinsic Viscosity).

The resulting pellets are consistently sized, and the melt flow has no dead zones, which effectively reduces hollow pellets and yellowing issues.

Efficient Degassing to Minimize PET Degradation Risk

Enhanced degassing performance through forced vacuum venting effectively removes moisture and volatile compounds.

This reduces the risk of thermal degradation, helping to preserve the molecular weight and intrinsic viscosity (IV) of PET.。

Flexible Process Adjustability for Varying Material Conditions

The system allows for flexible adjustment of screw combinations, thread configurations, temperature zones, and shear intensity.

This ensures compatibility with PET flakes of varying IV levels and different impurity contents.

Suitable for High-Filler, Modified, and Composite Pelletizing

Supports the direct addition of additive masterbatches, modifiers, and fillers to enhance material properties.

Enables efficient compounding of PET with other materials (e.g., glass fiber, flame retardants), making it ideal for specialized and functional applications.

How does a PET flake pelletizing machine work?

PET Flake Feeding

The cleaned PET flakes are fed into the pelletizing line through a feeding system, with a conveyor belt or feeder moving the flakes at a steady rate to the extruder inlet.

Melting and Extrusion:

After feeding, the flakes enter a twin-screw extruder, where the intermeshing screws provide additional mixing and homogenization. Inside the extruder, the PET is transformed into a viscous molten state.

The screw design and temperature profile are optimized for PET—typically featuring multiple heating zones and precise temperature control to ensure a uniform melt without thermal degradation. The screw rotation not only melts the PET but also thoroughly mixes it, ensuring that any additives (such as stabilizers or masterbatches, if added) are well dispersed.

Degassing (Venting)

As the PET melts, any residual moisture or volatile contaminants (such as trace solvents, monomers, or degradation byproducts) form bubbles. To remove these, vacuum degassing ports are installed on the extruder barrel. Typically, a PET pelletizing extruder has one or two vacuum venting sections, where pumps extract gases from the molten plastic.

Vacuum degassing is critical for PET: it prevents degradation caused by moisture and helps maintain the polymer’s molecular weight and intrinsic viscosity. By extracting steam and volatile compounds, the machine minimizes the risk of PET chain scission (which would lower the IV).

Melt Filtration System

After degassing, the fully molten PET is pushed into a melt filtration system (screen changer). The screen changer captures any remaining solid contaminants in the melt, such as paper labels, wood, unmelted plastic, or tiny metal fragments. Although PET flakes from the washing line are typically very clean, the filter provides a final safeguard to ensure pellet purity.

Depending on the level of contamination, different types of filters are available, such as plate filters, piston filters, and self-cleaning backflush filters.

Pelletizing (Cutting)

After filtration, the molten PET is extruded through a die head at the end of the extruder and cut into pellets by the pelletizing unit. There are several pelletizing methods, but a common one for PET is strand pelletizing:

In strand pelletizing, the melt exits the die in the form of long spaghetti-like strands, which are cooled (typically in a water trough) and then cut into pellets by rotating knives.

In water ring pelletizing, the die has multiple holes, and rotating knives cut the extruded melt at the die face; the pellets are thrown into a circular water ring chamber where they are cooled. (This method is generally not used for PET.)

In underwater pelletizing, cutting also occurs at the die face but is fully submerged in water, ensuring immediate cooling.

Cooling and Drying

In strand pelletizing, cooling is achieved by submerging the strands in a water bath before cutting. The mixture of pellets and water is then sent to a vibrating screener, which separates the water and screens out any oversized or fine particles, ensuring uniform pellet size.

Collection and Packaging

Finally, the dried pellets are conveyed by a blower into a product silo. From there, they can be packed into bags or large containers for transport. Some recycling lines feature automatic bagging stations capable of filling big bags with 500–1000 kilograms of pellets.

PLC Control System

Throughout the process, modern PET flake pelletizing machines are equipped with PLC control systems for automation. Operators set parameters (such as temperature, motor speed, vacuum level, and cutter speed) on a central control panel. Minimal manual intervention is required, aside from feeding flakes and collecting the finished pellets.

Types of PET Flake Pelletizing Machines

1. Single-Screw Extruder vs. Twin-Screw Extruder:

Single-Screw Pelletizer:

The single-screw extruder is mechanically simpler—with one screw inside the barrel. Historically, PET flakes needed to be crystallized and thoroughly dried before extrusion to avoid rapid IV loss, as the single screw has limited devolatilization capacity.

Advantages of single-screw machines include: generally lower cost, easier maintenance (fewer moving parts than twin-screw), and slightly lower power consumption per kilogram at smaller scales.

However, disadvantages compared to twin-screw include: weaker mixing and dispersing strength (which is crucial for thoroughly melting PET and additives), and generally lower vacuum degassing efficiency (twin screws offer more surface renewal for gas escape).

In addition, at high throughput, single-screw machines must be very large, which becomes expensive. In practice, single-screw PET pelletizing lines are typically chosen for small to medium capacity needs or where budget constraints make some performance trade-offs acceptable.

Twin-Screw Pelletizer:

Twin-screw extruders are known for excellent mixing, compounding, and devolatilization capabilities. For PET recycling, twin-screw systems have become very popular because they can more effectively handle material issues (such as moisture and viscosity).

Advantages of twin-screw pelletizers include:

Excellent material mixing and homogenization – the two screws thoroughly mix the melt, ensuring consistent melt quality and color. This reduces problems like uneven heating.

Enhanced degassing – PET melt degasses very effectively in twin-screw extruders, meaning pre-drying is often unnecessary.

Higher output from smaller machines – twin-screw extruders usually have higher throughput than single-screw machines of the same screw diameter when processing PET, due to strong mixing and heat transfer.

The disadvantages mainly relate to cost and complexity: twin-screw extruders are more expensive to manufacture (two screws, more complex gearbox), and maintenance is more complex (screw elements wear).

Nevertheless, for many medium- and large-scale PET recycling operations, twin-screw pelletizers remain the preferred solution because they produce the most consistent, high-quality pellets. These machines preserve PET’s intrinsic viscosity and ensure stable output, which is critical for downstream use in high-quality products.

2. Pelletizing Methods:

As previously mentioned, PET pelletizing lines can be equipped with different pellet cutting systems:

Strand Pelletizing:

A low-cost, simpler method. Best suited for lower throughputs (e.g., a few hundred kg/hour or less) and when skilled operators are available. It is less suitable for very large production lines, as managing many strands at high output is challenging.

Water Ring Pelletizing:

Moderate in complexity. Die-face cutters and the water ring can handle medium output and help control most of the mess. (Commonly used for soft plastic film pelletizing.)

Underwater Pelletizing:

A high-end method. Suitable for large-scale production (500 kg/hour to several tons/hour), and produces the most uniform pellets. It also has the advantage of immediately isolating the melt from air, which helps prevent any oxidation of PET at the die. The downside is that underwater cutting equipment and control systems are more expensive.

Boxin Machinery’s PET pelletizing lines come standard with strand pelletizing, with the option to upgrade to underwater pelletizing for those seeking higher automation and pellet consistency.

3. Other Specialized Types:

While single-screw and twin-screw systems cover the main distinctions, a few other variations are worth noting:

Twin-Screw Compounding Lines (Reactive Extrusion):

Some twin-screw pelletizers are designed not just for basic recycling, but also for adding modifiers or performing reactive extrusion (e.g., adding chain extenders during extrusion to boost PET IV). These lines feature side feeders for adding additives or fillers. They blur into compounding extruders but are relevant if the buyer intends to produce enhanced PET compounds (with glass fiber) or increase molecular weight through reactive chemistry during pelletizing.

Integrated Continuous SSP Systems:

A highly specialized, high-end type where pelletizing is combined with immediate Solid-State Polycondensation (a process that raises PET IV in solid pellet form). This is not common in standard machines but is an option for large-scale bottle-to-bottle recycling operations.

To decide on the type of PET pelletizing machine, consider the following factors:

Quality Requirements:

If maximizing IV and pellet quality is critical, a twin-screw extruder with excellent degassing and underwater pelletizing is recommended.

Budget:

Single-screw lines are more cost-effective. They can handle many applications—especially if the manufacturer has optimized the PET design. For medium budgets, a single-screw system with good vacuum capability can provide a reliable solution.

Material Form:

If handling inconsistent PET waste (e.g., thick lumps, preform runners, or molded PET chunks), twin-screw systems can process melting more evenly.

Maintenance & Skill Level:

Twin-screw machines require maintenance of both screws and tight tolerances; users with lower technical skills may prefer the simplicity of single-screw systems. On the other hand, many companies are already familiar with twin-screw maintenance, as it’s common in plastics recycling.

Custom OEM Services & Solutions

As a professional Pet Bottle Flakes Pelletizing Machine manufacturer in China, Boxin Machinery stands out in the industry with its OEM and custom engineering capabilities. For global B2B buyers, the ability of the system to adapt to local raw material conditions, regulatory requirements, and factory layout is a key factor in procurement decisions.

Tailored Engineering

• Raw material assessment (via sample analysis)

• Customized process flowchart and plant layout (CAD drawings)

• Modular equipment selection based on buyer priorities (cost, output, water resource constraints, etc.)

• Turnkey delivery including steel platforms, electrical wiring, piping, and control cabinet configuration

Pre-Sales Testing & Consultation

Clients can send PET bottle samples to Boxin’s R&D center for small-scale washing and contamination analysis. Based on the results, Boxin recommends a suitable system configuration considering:

Contamination type (glue, oil, label type)

Color ratios (clear, blue, green, or mixed)

Moisture levels and target IV retention of flakes

Global Installation & Training Services

Boxin offers on-site installation, commissioning, and operator training, as well as remote installation support via video calls. Buyers will receive:

• Electrical wiring diagrams

• Maintenance schedules

• Spare parts lists

• Operation manuals

After-Sales Technical Support

Boxin guarantees:

• One-year full machine warranty

• 24-hour technical response

• 48-hour dispatch for critical spare parts

• Lifetime maintenance guidance