In the course of the extrusion process, PET loses viscosity, which then may need to be increased in a subsequent process, namely polycondensation. In the same process, the granulate is decontaminated so as to be suitable for direct food contact.
Following extrusion, the granulate is also amorphous. It must be thermally crystallised in order to avoid formation of lumps, then it is treated for a selected length of time in the SSP reactor where it is subjected to heat and vacuum. The two factors temperature and time effect so-called polycondensation, a process in which H₂O and glycol are released, the molecule chains lengthened and the viscosity of the granulate increased.

Advantages of the Starlinger iV+ technology

• Energy savings: The entire system (extrusion and inline SSP) consists of a continuous or partially continuous process in which residual heat generated in various process steps is used in subsequent steps.
  
  
• FIFO: Both crystallisers and the SSP unit operate according to the FIFO principle (first in / first out). This ensures that each pellet undergoes the defined process time and parameters for the selected length of time.
  
  
• A modular system increases flexibility: A variable number of reactors is used depending on the desired IV increase and reactor time.
  
  
• Adjustable IV increase: The degree of IV increase is variable and is selected according to the planned used of the material and realised by determining the appropriate residence time in the reactor.
  
  
• Reduction of acetaldehyde content: The high decontamination capability of the SSP reactor after extrusion can reduce the AA content of the repelletised material to <1 ppm, a value like that of new material.
  
  
• Food contact: In June 2004, only one year after development of the unit was complete, the United States Food and Drug Administration confirmed in a Letter of Non-Objection that PET from recoSTAR PET iV+ lines is acceptable for 100 % use in direct food contact applications.