A step towards understanding plastic complexity: Antimony speciation in consumer plastics and synthetic textiles revealed by XAS

We identified the antimony species present in a wide variety of plastic samples by X ray absorption spectroscopy (XAS) at the Sb L3 edge. The samples contained different concentrations of antimony (Sb), ranging from PET bottles in which Sb compounds are used as catalysts, with concentrations around 300 mg/kg, to electrical equipment in which the element is used as a flame retardant, with concentrations of several tens of thousands of mg/kg. Although the shape of the spectra at the L3 edge is quite similar for all Sb reference materials, we were able to identify antimony glycolate or acetate in PET bottles, bound organic Sb in c-PET trays and senarmontite in electrical materials as the main Sb components. In samples with high Ca content (e.g., electrical objects, some c-PET food trays and textiles) the Ca Ka emission line interferes with the Sb La line by introducing a high background which reduces the signal-to-noise ratio in the Sb XAS spectrum, resulting in noisy and distorted spectra. The element-resolved map on a PET bottle sample revealed both Sb and Ca hot spots of around 10-20 microns in size, with no correlation.