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Reasons for the Discoloration of Postconsumer Poly(ethylene terephthalate) during Reprocessing
Author(s) -
Berg Dennis,
Schaefer Karola,
Koerner Andrea,
Kaufmann Robert,
Tillmann Walter,
Moeller Martin
Publication year - 2016
Publication title -
macromolecular materials and engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.913
H-Index - 96
eISSN - 1439-2054
pISSN - 1438-7492
DOI - 10.1002/mame.201600313
Subject(s) - antimony , materials science , polyamide , x ray photoelectron spectroscopy , ethylene , mass spectrometry , chemical engineering , nuclear chemistry , catalysis , composite material , chromatography , metallurgy , chemistry , organic chemistry , engineering
Gray and/or yellow discoloration may occur during repeated heating of poly(ethylene terephthalate) (PET). Both phenomena can cause problems in further application. In this work, the reasons for the discoloration of PET during reprocessing are investigated by physical and chemical analysis such as colorimetry, size exclusion chromatography, viscosimetry (η inh. ), inductively coupled plasma mass spectrometry, X‐ray photoelectron spectroscopy, and MALDI‐ToF‐MS analysis. It is found that the antimony content which originates from catalyst residues used in PET synthesis has high influence on the gray discoloration obtained during reprocessing of PET. Antimony ions are reduced to elementary antimony during heating to temperatures above 230 °C as proven by X‐ray photoelectron spectroscopy. The yellow discoloration is partially generated by polyamide contaminants which are used as barrier layers in PET packaging materials such as soft drink bottles. In conclusion, to prevent discoloration of postconsumer PET during reprocessing different methods such as oxidation of gray metallic antimony or sorting out of polyamide contaminants are needed.