**2. Parameters controlling the POSTC – PET mechanical recycling**

The main parameters controlling the POSTC-PET mechanical recycling are: the contamination level and the degradation degree.

#### **2.1 POSTC – PET contamination**

POSTC-PET contamination can be of the following three types: *macroscopic and microscopic physical contamination and chemical contamination.*

*Macroscopic physical contamination* of POSTC-PET is easy to clear off as it consists of dust, glass chops, stones, adhesives, product residues, plastics such as PVC and PE, earth impregnation due to improperly storage.

*Microscopic physical* c*ontamination* is more difficult to clear off especially because is partially attached to the bottle because it is about adhesive or other impregnated impurities resulted after abrasion or impact. These impurities break the thread either during granulation in the melt processing or during the spinning in the fibre industry. This leads to decrease the quality and productivity of the recycling.

*Chemical contamination* is the result of *adsorption* of flavouring, oil, pesticides, household chemicals, and fuel if the bottles were re-filled with such products in a secondary utilization. The proportion of POSTC-PET interaction with these compounds depends on the diffusion behaviour of contaminants and the sorption properties of the polymer. The removing of these contaminants implies *undergoing the reverse processes, namely desorption*. The adsorbed chemical impurities into the polymer *settle on the risk potential of* POSTC-PET mechanically recycled especially if the food packages are targeted. The recycling by desorption can not be considered because of its very low productivity, this process being an extremely slow one. For diminishing as much as possible the impurity content, the POSTC-PET melts are filtered during the mechanical recycling at extrusion, before passing throuth the nozzle, using particular filters (Yang Tang & Menachem, 2008).

POSTC - PET requests a severe control of the contamination level especially if it is recycled into food packaging. Currently, the impurity content limits are established and generally accepted for POSTC-PET recycling as food and non-food packaging (EGPMFC, 1999; Franz, 2004). The following limits of the POSTC-PET impurity residual content have been accepted for recycling as food packaging: 20 ppm or less metal, 10 ppm or less paper and 30 ppm or less polyolefins (Di Lorentzo et al., 2002; Hong JuZhou et al., 2007; Hong Jun Zhou et al., 2007 ). The framing into these limits depends on the technicality of the applied conditioning solution (sorting - washing etc), and by the legislative effort necessary for: the increasing of the population cooperation, the setting up of the infrastructure to analyze the impurity content down to the parts per million (ppm) level, the inspection on the law observance (Knit, 2002; David, 2001; Novis, 2003; ).
