Cleaning efficiency of poly(ethylene terephthalate) washing procedure in recycling process

This work demonstrates the poly(ethylene terephthalate) (PET) washing process, which is the very important step in the overall PET recycling procedure. The samples of waste PET bottles were washed in sodium hydroxide at two different temperatures, that is, at 70 and 75°C, at a time intervals of 15 and 30 min. The cleaning efficiency of the washing processes was determined through the identification of the residual impurities and products of PET degradation. The samples before and after the washing procedure were characterized by gas chromatography/mass spectrometry (GC/MS), gel permeation chromatography, thermogravimetric analysis and differential scanning calorimetry. Due to low obtained oligomer molecular masses, it can be concluded that the degradation during all washing processes is not strong. Results show good purity of washed PET, especially at 75°C, due to very low content of adhesives, toxic compounds and formed monomers. The washing process carried out at 75°C for 15 min can be considered as the most successful. It results with low polymer degradation and the removal of the high quantity of contaminants in short time interval.