Italian technology plast / April 2024 |
Figure 2 : Phenylcyclohexane evaporation temperature vs temperature and pressure
PET is the material that best benefits from this double treatment due to the high melting temperature .
LINE LAYOUT The Gamma Meccanica Compac DUV regeneration line consists of a vacuum reactor with Ecotronic technology for temperature control and lower consumption , an extruder with a special screw profile , a high capacity filter , a melt pump , an underwater pelletiser and finally an in-line crystalliser . The material is fed into the reactor through a dual hopper feeder equipped with special
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vacuum sealing valves . From the first hopper feeder , the material descends by gravity into the hopper feeder below where a vacuum is created and the material is ready to enter the reactor without altering the environmental characteristics of the reactor itself . In the reactor , the material is kept at a high temperature . In the case of PET , the temperature can range from 160 ° C to 190 ° C . In addition , high vacuum conditions ( up to 10 mbar ) are maintained in the reactor .
VACUUM SYSTEM TO EXTRACT MOISTURE The vacuum is used to extract moisture up to a maximum of 50-100 ppm . With these residual moisture values , the IV drop due to hydrolysis processes is practically nil . Thanks to the high vacuum , the water already evaporates at a temperature of 20 ° C . In addition , any polluting substances ( especially those included in the FDA and EFSA challenge tests ) evaporate at the high process temperatures and vacuum inside the reactor and are therefore extracted . In addition , the high temperature allows for greater migration of these substances and moisture from the inside to the outside of the material . For example , phenylcyclohexane , one of the pollutants included in the challenge test at ambient pressure , evaporates at 257 ° C , while in the DUV it evaporates at 125 ° C .
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With the DUV system , this substance , as well as the others in the challenge test , can be extracted with higher efficiency than the minimum required to obtain the EFSA approval for contact with food . Figure 2 shows the evaporation temperature of phenylcyclohexane vs temperature and pressure .
FILTRATION SYSTEM The extruder is equipped with a specific screen changer for PET processing . Filtration is of great importance because it eliminates any contaminants present in the material and can even eliminate particles down to 30 microns in size . The filter can be the batch or backflush type or a continuous filter of the latest generation . After filtration , the material enters the TI underwater pelletiser , which delivers pellets of the required size . If the need is for greater precision in the size of the final product , a melt pump can be added . An in-line crystalliser completes the DUV system , where the residual heat in the pellet is used to achieve crystallisation while saving energy . The cooled pellets ( after crystallisation ) enter a special centrifuge , then are stored in a silo , or loaded into big bags or other containers . In the end , a crystallised PET pellet is obtained with a negligible reduction in the original IV value ( from 0 to a maximum of 3 %) that , if necessary , can be used in contact with food .
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