How are plastic resins prepared before they are shaped into products?

Before plastic resins are shaped into final products, they typically undergo a process called compounding, which involves mixing raw materials according to a specific recipe. Resins are usually supplied to fabricators as pellets, flakes, powders, or sometimes as viscous liquids and suspensions.1

During compounding, various additives are incorporated to achieve desired product properties, including:

• Plasticizers: Used to improve flexibility and processing.12
• Fillers and Reinforcements: Materials like carbon black, silica, or fibers are added to enhance mechanical properties such as stiffness.23
• Colorants and Stabilizers: Mixed in to provide specific aesthetic or protective qualities.12

Mixing may be performed using dry blending, stirred tanks, or high-intensity internal mixers like the Banbury mixer, which applies significant heat and pressure to ensure a uniform mixture. In some manufacturing workflows, this mixing step is integrated directly into the extrusion or molding process. Depending on the material and the intended forming method, the resin may also be pre-compressed into a "biscuit" or prepared as a stable liquid suspension, known as a plastisol, before being introduced to the mold.145