Fluoropolymers are a unique class of per- and polyfluoroalkyl substances (PFAS) that occur as higher molecular weight solids with lower toxicological concern in contrast to nonpolymeric PFAS. When undergoing thermal degradation, however, fluorinated incomplete products of combustion are potentially released into the gas phase, thus being of potential environmental concern as well as for human exposure. In this study, thermal degradation of pre-characterized fluoropolymers (polytetrafluoroethylene, poly(chlorotrifluoroethylene) and Viton A) was conducted in a thermogravimetric evolved gas-analyzer combined with residuals collected onto a thermal desorption (TD) tube. Any products not retained by the TD tube were monitored using an in-line Fourier transform-infrared spectrometer. Contents of the TD tube was analyzed via gas chromatography-mass spectrometry for target and suspect PFAS. Experiments were conducted by ramping temperature from 25 °C to 950 °C at 20 °C/min. Major degradation products of the fluoropolymers included individual monomeric units of each fluoropolymer, like C₂F₄ and C₂ClF₃, with degradation complete (i.e., no change in mass) at approximately 500-600 °C. Degradation of a commercial Viton A left a solid residual after reaching a temperature of 950 °C. The residual underwent instrumental neutron activation analysis for total fluorine, powder x-ray diffraction for inorganic fluoride, and was extracted for liquid chromatography-quadrupole time-of-flight mass spectrometry for target, suspect, and nontarget PFAS analysis. While nonvolatile target PFAS were less than detection, a major product was CaF₂. Using lab-scale degradation studies to simulate open burning of fluoropolymers, a small-scale open burn apparatus was developed based on TD tubes for the capture of gas-phase PFAS and filters for particulate-bound PFAS. Identification and quantification of thermal degradation byproducts of fluoropolymers will aid in understanding the potential for human exposure and environmental impacts corresponding to the disposal of fluoropolymers by thermal processes.

Mitchell Kim-Fu

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