Recycled PET for Direct Food Contact
Recycled materials must satisfy stringent criteria to receive approval for direct contact with food in packaging. For this reason, most recycled PET is still converted into textile fibers. In Europe, only about 25 % of the PET reclaimed from used bottles is currently used to manufacture new PET bottles. A new multi-step process now permits reliable decontamination of recycled PET. In this process, the washed PET flakes are first dried, extruded and palletized. Next, the pellets are placed in a solid-phase reactor that is angled with respect to the horizontal axis of rotation. This creates a tumbling motion that mixes the free-flowing PET pellets gently and uniformly. The inside of the reactor can be evacuated down to a pressure of 0.1 mbar.
Through use of so-called challenge tests, it was possible to verify that there is no health risk from material treated in this way. In these tests, the starting material is first contaminated with a complex mixture of chemicals. The model contaminants simulate improper use of PET beverage bottles, for instance, storage of household chemicals prior to recycling. The mixture consists of both polar and non-polar substances, and contains volatile and non-volatile components.
When tracking material contaminated in this way through the course of the recycling process, it was found that the washing process removed only surface contamination. While some of chemicals that had diffused into the material were removed during extrusion, up to 60% of the initial amount of non-volatile components that had diffused into the material still remained in the pellets.
The process conditions in the tumbling reactor, however, give all chemicals time to defuse out of the pallet interior to below a level at which there is any health risk. In this way, chemicals adhering to the surface as well as those that diffused into the polymer were removed reliably.