Why is PET called Chip instead of Particle?

Common plastics are usually called “pellets,” but some plastics, such as PA nylon and PET polyester, are not called pellets. Instead, they have a more professional-sounding name, “Chips.” Why is this the case?

The biggest difference between Chip and Particle lies in molding shapes.

Common “particles” are cylindrical. Most plastics, such as PE, ABS, and PP, are molded into pellets. They are generally extruded into strips during pelletization and then cut into cylindrical shapes.

Water Pelletizing

Nylon (crystallized) and polyester(PES) are crystalline polycondensations with meager melt strength, making strip pelletizing impossible. Instead, they use underwater hot cutting or air-cooled cutting for pelletizing.

Air Cooling Cutting

The resulting pellets are flake-shaped, hence they are called “chips.” Therefore, chips generally refer to nylon, polyester, and other resins produced by polymer factories or resins modified with minor additives (e.g., PET chips modified with titanium dioxide to produce bright, semi-bright, and matte PET chips).

Typically, downstream modifications such as adding glass fiber (GF), fillers, or tougheners to nylon or polyester result in the material no longer being called chips but rather particles.

Commonalities Between Plastic Chips and Particles

We can observe that whether they are “pellets” or “flakes,” both have regular shapes and uniform sizes, making them “granular.” Their shape and size differentiate them from “powders” and “shavings.”

They also have the following advantages:

Production Convenience: Pellets can easily enter the screw, be melted, plasticized, and then molded. In general, plastic raw material transportation mainly relies on vacuum. During the transportation and processing of powders, the loss can be quite significant. Large, irregular shavings often cause “bridging” at the feed inlet, affecting continuous production. However, some products must use powder due to process limitations.

Transportation Convenience: Pellets are easier to transport. They can be easily bagged and loaded onto trucks for transportation. In contrast, many powder materials are hygroscopic. The large surface area of powder makes it more prone to clumping and even degradation, which is detrimental to processing. Large, irregular scraps, on the other hand, take up much more volume for the same weight.

Ease of Use: When using plastic pellets, the granular form allows for uniform heating and better plasticization, facilitating subsequent mixing with other additives and producing a smooth end product.

Fast Reaction Speed: The molding of polymer materials often involves more than just physical actions. The diffusion path of small molecule products within small particles is shorter than in large particles, making it easier to remove them. Additionally, smaller sample particles have a larger total surface area, increasing heat transfer rates and reaction speeds. Therefore, within a certain range, the reaction speed is inversely proportional to the size of the raw material particles. However, if the particles are too fine, they may agglomerate, adversely affecting the reaction speed. Hence, granular form is generally preferred when manufacturing materials.