TWIN SCREW EXTRUSION SYSTEMS TO PROCESS BIO- BASED ...

the process is amenable, die face pelletizing is often preferred for high volume and
reclaim applications.
Air quench die-face pelletizing is used for highly filled or viscous formulations, such as a
fractional melt HDPE with a natural fiber, such as rice hull. After the cut, pellets are
pneumatically conveyed to either a vibratory cooler/separator or fluidized vibratory unit,
where cooling is finished. Additional product drying is possible via a heated air stream
in the fluidized bed. Most formulations cannot be processed in this method, as many
materials tend to smear at the die face. Vortec tubes to direct chilled air at the die
face and/or atomizers to mist the cutting chamber can be used for borderline
formulations. Pellets produced via the air quench method are typically slightly deformed
in cooling, and are generally deemed not as aesthetically appealing as others.
Underwater pelletizing is exactly what the name describes. The molten product is fed
through a die with a series of holes in a circular pattern. When the product emerges from
the die, it is cut into pellets by the rotating blades and immediately quenched in water.
The water/pellet slurry is then pumped to a spin dryer for dewatering and surface drying.
This system produces a unique spherical pellet resulting from the product being cut in a
submerged environment. Underwater pelletization is often used for PLA formulations.
HSEI twin screw extruder with underwater pelletizing system