The purpose of removing moisture from plastics is to obtain a quality product. The defects caused by insufficiently dried raw material are usually invisible to the naked eye, yet they directly affect mechanical strength and final quality.
Plastics are usually produced in pellet form and absorb moisture from the atmosphere. If not dried, plastic can undergo hydrolysis depending on its type, and undesirable changes occur in its physical properties. Removing moisture before processing prevents cosmetic defects (splay / silver streaking), avoids hydrolysis and helps prevent part failures.
Hygroscopic polymers (ABS, acrylic, PET, PBT, polyurethane, polycarbonate, etc.) absorb moisture internally and release it into the air; drying them is essential, and internal moisture cannot be removed by hot air alone. Non-hygroscopic polymers (PVC, PP, PS, PE) do not take up moisture internally but may carry moisture on the surface; in this case, applying heat is sufficient to remove surface moisture.
It is important to follow the appropriate temperature and time during pre-drying; drying carried out at too low a temperature may fail to remove moisture to the desired level, even if it takes a long time.
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