Plastic Coloring Modification and Pumping Procedure

Before being molded, plastic materials usually come in the form of small pellets, which are often referred to as “plastic pellets.” However, these pellets are not produced in a simple, egg-like shape as you might imagine.

In reality, plastic pellets are made from petroleum derivatives that go through a specific process. The liquid plastic is melted, then cooled, and drawn out into long, cylindrical strands before being cut into small pellet-sized pieces. So, what you see as plastic pellets are actually cylindrical, not perfectly round! This process of turning petroleum products into small plastic pellets is called the pelletizing process.

Typically, plastic pellet manufacturers produce single types of plastic. For example, a production line for polycarbonate (PC) only produces PC pellets, while an acrylic production line only produces acrylics. But what about ABS? ABS is actually a blend of three types of plastic: acrylonitrile, butadiene, and styrene, which are mixed together in specific ratios. Even though ABS consists of multiple plastics, the final product is a single type of pellet.

This blending and pelletizing process, which involves various chemical reactions, is called “plastic modification.” By mixing different types of plastics, their properties change, and the process of melting and reshaping them into new pellets is known as “compounding.” Understanding the chemical structure of these plastics is crucial for optimizing their properties during compounding. In ABS production, for example, some manufacturers pre-mix certain components before compounding them with others.

PC/ABS is made by melting and mixing PC and ABS together before pelletizing. However, it’s important to note that when plastic pellets are compounded, their physical properties can degrade. The process involves pushing the molten plastic through a screw extruder, which can break the original long polymer chains into shorter ones, making the plastic molecules less entangled, and thus, weaker and more brittle.

Another challenge is that some companies intentionally add low-quality recycled materials (regrind resin) during the coloring or modification process to cut costs, which further degrades the plastic’s mechanical properties. This can result in brittle plastic products, even if you’ve taken steps to prevent the addition of regrind resin during molding. Therefore, it’s crucial to trace the issue back to the raw material suppliers and implement strict quality controls for incoming plastic pellets. A cost-effective way to monitor pellet quality is by testing their Melt Flow Index (MFI). Evaluating the material properties, such as strength and durability, is also essential to ensure high-quality end products.