Dehumidifying of plastics resin is utilized to minimize or eliminate problems that may be caused by too much or too little moisture in a plastic material during processing. Although most processors accept the need to predry resins, particularly highly hygroscopic ones, many do not understand the basics - or even the vocabulary of resin drying.
The extent to which moisture affects the quality of a molded or extruded part is determined by the specific plastic resin being processed and the intended purpose of the part. Regardless, it is highly probable that improper or incomplete drying of the raw material will create problems, whether during processing or when the product is in use, or worse - both.
We use the topics below to help form a guide to understanding the basics of dehumidifying plastic materials as well as the esthetic and performance issues that present from improper drying.
Heat causes the molecules to move about more vigorously, weakening the forces that bind the water molecules to the polymer chains. Above certain temperatures, the force that binds the water molecules to the polymer chains are reduced permitting free movement of the molecules to aid the drying process