What Is Pelletizing?

Pelletization converts original and recycled polymers into small, uniform pellets that serve as the raw material for manufacturing new plastic products. 

Pelletization makes plastic feedstocks easier and more efficient to handle and ensures consistent results during mixing and forming. 

Read on to learn more about why leading manufacturers prefer high-quality pelletized primary or recycled polymers, how the pelletization process works, and why choosing the right cutting equipment matters.

Roll With It: Plastics and Pelletizing

Pelletizing creates a precisely formed plastic feedstock with the perfect size, composition, and integrity for your specific manufacturing process or consumer end-use. Producing pellets at scale with the quality and consistency demanded by an industry takes expertise, experience, and specialized machinery and parts — including precision-engineered industrial blades.

Below we take a close look at what pelletization is, when and where it is used, and some of the benefits it offers processors and consumers. We also examine the critical role played by rotor knives in ensuring quality and consistency across a wide range of pelletization applications.

Why Pelletize?

Pelletization is widely used to make feedstocks and bulk consumer products easier to handle, transport, and store. In the upstream plastics industry, pelletization offers a solution to many of the problems associated with more traditional “raw” feedstocks: 

• High levels of waste: Powdered, granular, or flaked plastic feedstocks are susceptible to spillage, static buildup, and trapping during processing.
• Inefficient handling: Fine or inconsistent feedstocks are harder to move and handle.
• Inaccurate mixing: Looser feedstocks are harder to mix accurately
• Unpredictable melting: Fine materials expose less of their surface area to heat
• Limited customizability: The bulk handling systems required to handle fine or flaked feedstocks make it harder to produce smaller batches of feedstock with specific properties such as UV resistance, flame retardancy, or impact strength.

Pelletization offers an effective solution to these challenges by bringing consistency, convenience, and predictability to feedstock handling and processing.

How Does Pelletization Work?

The production process for plastics feedstocks like polypropylene polyethylene and PVC is pretty uniform. It involves combining raw synthetics or recycled plastics and then heating and melting these to produce a polymer with specific properties.

Pelletizing involves instead extruding the melted polymer mix as threads that are then cut and formed into beads of a uniform size. There are distinct ways of doing this, but they all involve fine control of the extrusion process and precision forming of the rapidly cooling pellets.

The resulting pelletized plastic feedstock offers superior size consistency and better handling and processing characteristics than other types of recycled or primary feedstocks. 

Pelletization technologies are also better for small batch processing, making it easier to produce feedstocks with customized colors or other characteristics including strength properties and stress- or UV-resistance.

Benefits of Plastics Pelletization

Pelletization comes with benefits that are critical to plastics’ performance in a wide range of applications. These include:

• Improved performance: Better feedstock mixes, improved quality control, and more targeted applications all boost product performance.
• Reduced waste: More consistency means more predictable handling conditions, and less material loss to spillage, entrapment, or static sticking.
• More efficient handling: Plastic pellets make bulk handling and transfer easier with consistent flow characteristics and predictable stackability.
• Efficient processing: Different feedstocks can be precisely combined. The right size pellet exposes the optimum surface area for precisely controlled downstream melting and extrusion.
• Customizable properties: Smaller batch processing makes it possible to produce pellets with the right properties for your customers’ most specialized needs.

What is a Plastics Pelletizer?

The heart of the pelletization process is the pelletizer machine itself. While specific designs vary, you must control the integrity, surface characteristics, and size of particles as they form. To do this conditions inside the unit must be carefully managed. 

Depending on the kind of plastics being handled, including complex recycled materials and highly specialized polymers, producers use one of several types of pelletization technology:

Strand Pelletizers 

Strand pelletizers are used to handle most common thermoplastics. Here, molten plastic is extruded through a die, forming continuous strands. These strands are then pulled or conveyed through a rotating knife system. 

The rotating knives cut the strands into uniform pellets as they pass by, producing consistent pellet sizes. The pellets are then cooled, dried, and collected for further processing.

Underwater Pelletizers

Underwater pelletizers are used for heat-sensitive plastics. Molten plastic is extruded directly into a water-filled tank where it is cut into pellets by a submerged rotating knife. The water cools and solidifies the pellets, helping to control pellet size. Pellets are then drained and dried before packaging.

Air-Cooled Strand Pelletizers

Air-cooled strand pelletizers are similar to traditional strand pelletizers but protect heat-sensitive plastics where low moisture content is important. Extruded molten plastic is cut into strands and passed through a cooling chamber where ambient or chilled air cools them. The strands are then further processed to produce uniform pellets. 

Die Face Pelletizers

Die face or water ring pelletizers are used for polymers with low-melting points or highly viscous properties. Here, molten plastic is extruded onto a rotating cutting knife that slices the plastic into uniform pellets as it contacts the surface. The pellets are then rapidly cooled by immersion in a circulating ring of chilled water, before drying. 

Rotary Pelletizing Knives

Effective pelletization is heavily dependent on tough, durable industrial cutting knives made from hardened steel carbides of Stellite. These hard-working blades need to be optimized to the needs of the pelletization process and the specific machine they are installed in, as well as the characteristics of the polymer mix being processed. 

Both rotary and circular knives are key consumables in the pelletizing process and a significant operating expense for the operator. While cut-price replacement blades can help keep costs lower, working with an industrial knife company that specializes in premium pelletizer blades ensure optimum pelletizing performance for longer, including:

• The right blade for your machinery is always on hand
• Less downtime and lower maintenance costs
• Longer machinery life

Choose Hyde PDK Knives for Pelleting Performance

With over 140 years of experience, Hyde Industrial Blades is a leading manufacturer of pelletizer rotor knife solutions for the plastic production and recycling sector. Our industry-leading PDK solid rotors remain the go-to choice to meet the tough demands of strand plastic processing and other applications.

PDK knives offer:

• Superior wear resistance — of up to five times the life of comparable products
• Individually replaceable knives for the lowest total cost
• Interchangeable with solid rotors without any modifications to the pelletizer
• Fully reconditioned rotor body and wedges can be reconditioned after years of service to extend the life of the assembly

At Hyde, we can fully refurbish any rotor that we make (including those made by others) —whether it’s a straightforward sharpening or repairing damaged edges, and we stock a huge range of replacement rotors in a variety of widths and diameters and materials, for quick turnarounds and minimum process downtime.