Characterization of PFAS air emissions from thermal application of fluoropolymer dispersions on fabrics

ABSTRACT

During thermal processes utilized in affixing fluoropolymer coatings dispersion to fibers and fabrics, coating components are vaporized. It is suspected that per- and polyfluoroalkyl substances (PFAS) from the dispersions may undergo chemical transformations at the temperatures used, leading to additional emitted PFAS thermal byproducts. It is important to characterize these emissions to support evaluation of the resulting environmental and health impacts. In this study, a bench-scale system was built to simulate this industrial process via thermal application of dispersions to fiberglass utilizing relevant temperatures and residence times in sequential drying, baking, and sintering steps. Experiments were performed with two commercially available dispersions and a simple model mixture containing a single PFAS (6:2 fluorotelomer alcohol [6:2 FTOH]). Vapor-phase emissions were sampled and characterized by several off-line and real-time mass spectrometry techniques for targeted and nontargeted PFAS. Results indicate that multiple PFAS thermal transformation products and multiple nonhalogenated organic species were emitted from the exit of the high temperature third (sintering) furnace when 6:2 FTOH was the only PFAS present in the aqueous mixture. This finding supports the hypothesis that temperatures typical of these industrial furnaces may also induce chemical transformations within the fluorinated air emissions. Experiments using the two commercial fluoropolymer dispersions indicate air emissions of part-per-million by volume (ppmv) concentrations of heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether (Fluoroether E1), as well as other PFAS at operationally relevant temperatures. We suspect that E1 is a direct thermal decomposition product (via decarboxylation) of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoic acid (commonly referred to as HFPO-DA) present in the dispersions. Other thermal decomposition products, including the monomer, tetrafluoroethene, may originate from the PFAS used to stabilize the dispersion or from the polymer particles in suspension. This study represents the first researcher-built coating application simulator to report nontargeted PFAS emission characterization, real-time analyses, and the quantification of 30 volatile target PFAS.

Implications: Thermal processes used to affix fluoropolymers to fabrics are believed to be a source of PFAS air emissions. These coating operations are used by many large and small manufacturers and typically do not currently require any air emissions control. This research designed and constructed a bench-scale system that simulates these processes and used several off-line and advanced real-time mass spectroscopy techniques to characterize PFAS air emissions from two commercial fluoropolymer dispersions. Further, as the compositions of commercial dispersions are largely unknown, a model three-component solution containing a single PFAS was used to characterize emissions of multiple PFAS thermal transformation products at operationally relevant conditions. This research shows that fluoropolymer fabric coating facilities can be sources of complex mixtures of PFAS air emissions that include volatile and semivolatile PFAS present in the dispersions, as well as PFAS byproducts formed by the thermal transformation of fluorocarbon and hydrocarbon species present in these dispersions.

Acknowledgment

Portions of this work were supported by EPA contract 68HERC20F0377-001 with Jacobs Technology Inc. The authors are grateful to Josh Varga, Mike Tufts, Preston Burnette, Peter Kariher, and William Roberson for their assistance in the design, construction, maintenance, calibration, and operation of the string reactor. The authors acknowledge the unfortunate passing of our colleague Theran Riedel, without his innovations this work would not have been possible. The research described in this article has been reviewed by the U.S. EPA Center for Environmental Measurement and Modeling and approved for publication. The views expressed in this article are those of the authors and do not necessarily represent the views or policies of the U.S. Environmental Protection Agency nor does mention of trade names or commercial products that constitute endorsements or recommendations for use.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are openly available on ScienceHub at http://doi.org/10.23719/1527849 reference number D-g4fk.

Supplementary data

Supplemental data for this paper can be accessed online at https://doi.org/10.1080/10962247.2023.2192009.

Additional information

Notes on contributors

Lindsay C. Wickersham

Lindsay C. Wickersham was a Physical Scientist with U.S. EPA’s Office of Research and Development in the Air Methods and Characterization Division. Since the research of this work was performed, she has transitioned to a new position as a Physical Scientist with the Air and Radiation Division of U.S. EPA’s Region 9 Office. Lindsay has a research background in antimicrobial resistance in waterways, salivary assays, and PFAS incineration.

James M. Mattila

James M. Mattila is an ORISE postdoctoral scholar at the U.S. EPA Office of Research and Development. His work currently focuses on performing online mass spectrometry measurements of airborne PFAS.

Jonathan D. Krug

Jonathan D. Krug is an Environmental Engineer with U.S. EPA’s Office of Research and Development in the Air Methods and Characterization Division. His current research focuses on thermal treatment of PFAS and methods for determining effectiveness of treatment.

Stephen R. Jackson

Stephen R. Jackson is a Chemist with U.S. EPA’s Office of Research and Development in the Air Methods and Characterization Division. His research focuses on source characterization methods development and nontargeted analysis of polar and nonpolar organic samples.

M. Ariel Geer Wallace

M. Ariel Geer Wallace is a Chemist with U.S. EPA’s Office of Research and Development in the Air Methods and Characterization Division. Her research focuses on methods development for thermal desorption-gas chromatography/mass spectrometry applications to detect and quantify volatile organic compounds and emerging contaminants in air emissions.

Erin P. Shields

Erin P. Shields is a Physical Scientist with U.S. EPA’s Office of Research and Development in the Air Methods and Characterization Division. His research area involves developing methods to characterize source emissions and to evaluate pollution control devices.

Hannah Halliday

Hannah Halliday is a Physical Scientist with the U.S. EPA’s Office of Research and Development in the Air Methods and Characterization Divison. She specializes in non-targeted measurements of volatile organics.

Emily Y. Li

Emily Y. Li is a Research Chemist with U.S. EPA’s Office of Research and Development in the Air Methods and Characterization Division. Her current research focuses on developing methods for characterization and mitigation solutions for air pollutant sources to assess and control emerging air emissions.

Hannah K. Liberatore

Hannah K. Liberatore is a Physical Scientist with U.S. EPA’s Office of Research and Development in the Air Methods and Characterization Division. Her current research focuses on characterization of source emissions and environmental contaminants through nontargeted analysis.

Stanley (Mac) Farrior

Stanley (Mac) Farrior (CSS-Inc.) is a Fabrication Specialist that supports U.S. EPA’s Office of Research and Development. He specializes in design and fabrication of unique solutions enabling researchers to pursue relevant environmental questions.

William Preston

William Preston (CSS-Inc.) is an Analytical Chemist and Task Order leader for the Analytical Support Laboratory that supports U.S. EPA’s Office of Research and Development. Mr. Preston specializes in method development and method implementation that characterizes emerging source and ambient volatile and/or semi volatile organic emission profiles.

Jeffrey V. Ryan

Jeffrey V. Ryan is a Senior Research Chemist with EPA’s Office of Research and Development in the Air Methods and Characterization Division. His research focuses on method development to characterize source emissions of pollutants of emerging concern.

Chun-Wai Lee

Chun-Wai Lee, Ph.D., retired from EPA’s Office of Research and Development as a Senior Research Scientist in the Air Methods and Characterization Division. His research focuses on emissions and control of hazardous air pollutants from combustion and industrial sources.

William P. Linak

William P. Linak, Ph.D., is a Senior Research Engineer with EPA’s Office of Research and Development in the Air Methods and Characterization Division. His research focusses on the formation, emissions, and control of air pollutants from combustion processes.