Speciation of Antimony in PET Bottles Produced in Japan and China by X-ray Absorption Fine Structure Spectroscopy

Abstract

The oxidation state and coordination environment of antimony (Sb) incorporated into polyethylene terephthalate (PET) bottles were estimated based on X-ray absorption fine structure (XAFS) at Sb K-edge. Prior to XAFS analyses, Sb concentrations in 177 PET bottles collected in Japan and China were determined, showing that 30.5% and 100% of Japanese and Chinese PET bottles, respectively, contained more than 10 mg/kg of Sb. Most of the bottles used for aseptic cold filling and carbonated drinks contained a larger amount of Sb. Extended X-ray absorption fine structure (EXAFS) showed that the first neighboring atom of Sb in PET was estimated to be oxygen with a coordination number of about three. In addition, the contribution of Sb to Sb shell was discounted in the EXAFS, showing that Sb was not present as Sb2O3 in PET, although Sb was initially added as Sb2O3 in the production of PET. This information is consistent with the coordination environment estimated from the polycondensation reaction catalyzed by Sb, where Sb can be present as either Sb glycolate or Sb glycolate binding to the end group of the PET polymer. X-ray absorption near-edge structure (XANES) showed that Sb(III) initially added as Sb2O3 into PET was partially oxidized and the Sb(V) fractions reached approximately 50% in some samples. However, the oxidation state and coordination environment of Sb in PET had no relationship with the concentrations of Sb that leached into water from PET. Based on the present XAFS results and previous studies on the effects of temperature and others, it was concluded that the leaching behavior of Sb into water is primarily due to the degradation of PET itself, but is not related to the Sb species in the PET bottles.