PETpla.net Insider 06 / 2019

MATERIALS / RECYCLING PET planet Insider Vol. 20 No. 06/19 www.petpla.net 43 In order to describe the initial situation exactly, various PET flake samples were measured from the market in comparison to virgin mate- rial. Table 2 shows the results. Material Colour / Appearance N2-Content in ppm N Virgin PET (Invista) colourless, transparent <10 - NN PET flakes colourless, transparent 30 – 60 PET flakes dark blue 180 PET flakes colourful 215 Table 2: Nitrogen content of different PET materials from the market The influence of the process pres- sure during vacuum extrusion was car- ried out on an MRS-90 from Gneuss Kunststofftechnik. The usually applied process pressure of 25mbar at a throughput of 500kg/h was compared with process pressures of 5mbar and 1mbar. The results are shown in table 3 (all analysis results are averaged from several test series). Of particular interest is the fact that in the spray condenser used to protect the vacuum pump, the nitro- gen equivalents removed from the polyester analytically gave a conclu- sive material balance. When assessing the results, it should be borne in mind that the con- tent of nitrogen is to be understood as the sum-indicator and does not allow a clear conclusion on the nature of the nitrogen-containing additives. For a better understanding, these results are shown graphically in fig. 1. Fig. 1: Graphical representation of nitro- gen content (in ppm N) in correlation to process vacuum (in mbar) The results show that especially in the pressure range between 5mbar and 1mbar a significant improvement in decontamination could be observed, which allows the conclusion that with the large melt surface and the associ- ated high renewal rate of the surface, the MRS extrusion system offers consider- able advantages in the processing of PET bottle flakes in the deep vacuum range. In addition to the test results issued by the FDA and EFSA that the MRS meets the criteria of the challenge test, the application of process pressures in the range of 1-5mbar with the MRS from Gneuss Kunststofftechnik provides a process that efficiently removes foreign substances enriched in circulation pro- cesses in particular. As a general conclusion of this work, the demand can be derived that both the B2B processes on the market and the processes for preform produc- tion are to be improved or optimised in such a way that the repeated use of AA scavengers can be dispensed with. www.polyester-technology.com Material Colour/Appearance N2-content in ppm N Process pres- sure 25mbar Process pres- sure 5mbar Process pres- sure 1mbar Virgin PET (Invista) colourless, transparent <10 - NN - - - PET flakes colourless, transparent 30 – 60 30 – 55 25 – 50 15 – 35 PET flakes dark blue 180 165 155 130 PET flakes colourful 215 195 160 120 Table 3: Nitrogen content in correlation to process vacuum