Virgin PET
Virgin PET is usually in a crystalline state (indicated by its white color) when it is purchased from a supplier. It must be dry prior to processing. Using conventional desiccant drying systems, you should dry PET at 300 - 350˚ F. at a dew point of -20 to -40˚ F. for a period of 4 to 6 hours. This reduces the moisture content to .005% or below, ensuring production of a good product.
Reground PET
Regrind PET material is usually not crystalline, but amorphous and clear in color. A characteristic of amorphous materials is that they tend to soften and agglomerate at normal drying temperatures, forming clumps and adhering to the walls of a drying hopper. Crystallize amorphous material, prior to drying, to prevent this agglomeration from occurring. Agitating the material while heating it to a temperature of about 180˚ F will convert the material from its amorphous state to a crystallized state, ready for drying. We call this process crystallizing but technically, it is a re-crystallization of the material. Different formulations of PET have different rates of crystallization, ranging up to one hour. Note that if the regrind PET is white in color, it is probably already crystalline and may be dried as-is.
There are a couple of methods used for the crystallization/drying process.
See PET Desiccant Wheel Energy-Saver Dryer and Infrared Crystallizers/Dryers.
Biaxially oriented bottle scrap, regardless of color, is crystalline and should be further crystallized prior to drying – for safety sake.