A lot depends on the type of material we are discussing. The process of crystallizing merely involves the introduction of heat at about 250-300°F. If the resin is heated for a period of time, it will crystallize. As the resin crystallizes, it goes through its glass transition phase and gets very sticky. This crystallization process works well in the agitated hopper of a crystallizer or in an IRD (Infrared Dryer). However, if you try to crystallize PET in a standard dryer hopper this can lead to serious problems as the material sticks together and turns quite hard.

Some regrinds are worse than others. Preform, sheet and APET (pelletized amorphous) materials generally require crystallizing in an agitated hopper or IRD, prior to being introduced to the drying hopper, at rates above 20%. The agitator in the crystallizer and the IRD rotation keeps the resin in motion and limits any sticking issues.

However, there are some PET grades that don’t tend to get sticky, like PCR (post consumer regrind) that is bi-axially oriented and does not tend to get sticky.

With a better understanding of the grade, we could offer a more specific response.

Mark Haynie
Sales Manager, Dryer Products

Novatec, Inc.