Recycling packaging materials 505 23. 4.2 Cleaning efficiency of conventional recycling processes Post-consumer PET which are going into packaging applications are usually recycled with super-clean recycling processes. However, these processes use conventional washing steps as well as several deep-cleansing steps in order to eliminate undesired post-consumer substances from the PET polymer matrix Therefore the cleaning efficiency of conventional washing processes is of interest because it influences the input concentration of post-consumer substances in feedstock material going into the deep-cleansing processes In the literature there are a few studies on the cleaning efficiency of ntional recycling processes. These processes contain washing and surface steps followed in some cases by remelting of the post-consumer I. Komolprasert and Lawson determined the influence of NaOH concentration, mixer speed and temperature on removal of the surrogate tetracosane from spiked PET. In this study percentages of residual tetracosane in the Pet flakes which were washed in small-scale experiments using 13 different conditions were determined. The results show that the tetracosane concentration in the washed flakes was 1. 4 to 3.3% of the initial spiked level As a result only mixer speed and temperature showed a significant effect on removal of the surrogate tetracosane from the PET flakes, while the effect of NaoH concentration was insignificant. The percentage of non-volatile hydrocarbon residues in washed PET flakes varies with the initial concentration. The study determined a removal of 89 to 97% of each hydrocarbon by washing. In a second study Komolprasert and Lawson determined the effect of washing and drying on the removal of surrogates in spiked PET flakes as well as in spiked PET bottles. They concluded that the combination of washing and drying removes 97 to 99% of the organic surrogates from the spiked PET bottles. The copper concentration was found to be 21% of the initial concentration after washing and drying(remark: the low cleaning efficiency for the copper organic compound is most probably due to the instability of this surrogate. It reacts during recycling to Cuo which cannot be removed. This behaviour shows that metal organic compounds are in general unsuitable as surrogates for challenge tests). In case of spiked PET flakes washing and drying removes more than 99% of the initial concentration of the organic surrogates. The high cleaning efficiencies of conventional washing and drying processes are most probably due high temperatures applied during the rying step and due to the fact that contaminants rarely penetrate more than a few u m into the polymer surface. This is in agreement with the result that the initial concentrations of the surrogates in spiked bottles are much lower than those in flakes, because the surface area of flakes is higher than in bottles. A third study from Komolprasert et al. evaluates the decontamination by remelting in a laboratory extruder. The results show that remelting can further reduce the contamination of spiked PET. However, from the data given in this paper, the amount of this reduction is very difficult to evaluate, because of the fact that the some of the applied surrogates(diazinon, malathion, metal organic copper compound)are not stable during extrusion. In addition volatile23.4.2 Cleaning efficiency of conventional recycling processes Post-consumer PET which are going into packaging applications are usually recycled with super-clean recycling processes. However, these processes use conventional washing steps as well as several deep-cleansing steps in order to eliminate undesired post-consumer substances from the PET polymer matrix. Therefore the cleaning efficiency of conventional washing processes is of interest because it influences the input concentration of post-consumer substances in feedstock material going into the deep-cleansing processes. In the literature there are a few studies on the cleaning efficiency of conventional recycling processes. These processes contain washing and surface drying steps followed in some cases by remelting of the post-consumer material. Komolprasert and Lawson15 determined the influence of NaOH concentration, mixer speed and temperature on removal of the surrogate tetracosane from spiked PET. In this study percentages of residual tetracosane in the PET flakes which were washed in small-scale experiments using 13 different conditions were determined. The results show that the tetracosane concentration in the washed flakes was 1.4 to 3.3% of the initial spiked level. As a result only mixer speed and temperature showed a significant effect on removal of the surrogate tetracosane from the PET flakes, while the effect of NaOH concentration was insignificant. The percentage of non-volatile hydrocarbon residues in washed PET flakes varies with the initial concentration. The study determined a removal of 89 to 97% of each hydrocarbon by washing. In a second study Komolprasert and Lawson16 determined the effect of washing and drying on the removal of surrogates in spiked PET flakes as well as in spiked PET bottles. They concluded that the combination of washing and drying removes 97 to 99% of the organic surrogates from the spiked PET bottles. The copper concentration was found to be 21% of the initial concentration after washing and drying (remark: the low cleaning efficiency for the copper organic compound is most probably due to the instability of this surrogate. It reacts during recycling to CuO which cannot be removed. This behaviour shows that metal organic compounds are in general unsuitable as surrogates for challenge tests). In case of spiked PET flakes washing and drying removes more than 99% of the initial concentration of the organic surrogates. The high cleaning efficiencies of conventional washing and drying processes are most probably due high temperatures applied during the drying step and due to the fact that contaminants rarely penetrate more than a few  m into the polymer surface. This is in agreement with the result that the initial concentrations of the surrogates in spiked bottles are much lower than those in flakes, because the surface area of flakes is higher than in bottles. A third study from Komolprasert et al. 17 evaluates the decontamination by remelting in a laboratory extruder. The results show that remelting can further reduce the contamination of spiked PET. However, from the data given in this paper, the amount of this reduction is very difficult to evaluate, because of the fact that the some of the applied surrogates (diazinon, malathion, metal organic copper compound) are not stable during extrusion. In addition volatile Recycling packaging materials 505