In this pelletizing and crystallization process, crystallization of the PET is accomplished utilizing the latent heat energy present in the pellets. The equipment line-up is similar to a traditional polymerization and extrusion line. However, the critical difference lies in the cooling of the polymer after it exits from the extruder die. An underwater pelletizing system is generally used. The pellets leave the dryer and enter the crystallization conveyor at an average temperature of more than 135 °C. Here the superficially cooled pellets are kept in constant motion, thus triggering the crystallization process which proceeds from the core to the outside of the pellet without needing any additional energy other than the latent heat energy present therein. A 40% degree of crystallization is achieved in this way.
Compared to conventional extrusion equipment for the manufacture of PET pellets, the technology achieves energy savings of around 20 %. A further energy saving of around 5% results during subsequent processing of the pellets in an injection molding machine.
Achema 2012 Hall 5.0 – B2
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