Science Inventory

Characterization of PFAS Air Emissions from Simulated Thermal Fabric Application Processes

Citation:

Wickersham, L., J. Mattila, J. Krug, S. Jackson, M. Wallace, E. Shields, H. Halliday, E. Li, H. Liberatore, S. Farrior, W. Preston, J. Ryan, C. Lee, AND W. Linak. Characterization of PFAS Air Emissions from Simulated Thermal Fabric Application Processes. JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION. Air & Waste Management Association, Pittsburgh, PA, , NA, (2023). https://doi.org/10.1080/10962247.2023.2192009

Impact/Purpose:

Many fabrics and products are coated with fluorinated dispersions; they provide strength, waterproofing, and durability to the product it is applied to. Industrial facilities bind this dispersion to fabrics by exposing them to three different temperatures ranging from 100°C up to 330°C to create a coating. Emissions from this industrial process have limited emissions controls and are not well understood. This product explores the direct emissions and transformation products created by this industrial heating process through use of a bench-scale fabric coating tower created by the EPA. Two commercially available fabric coating dispersions and a simple three component mix containing only one fluorinated compound were evaluated. Multiple analytical techniques were used to characterize the emissions from each heating zone and it was discovered that transformation of fluorinated compounds can occur at typical industrial temperatures. This research is of interest to industrial fabric coating facilities, state and local air districts, community leaders, and EPA as it identifies a potential source of PFAS compounds to the air, as well as highlights EPA’s toolkit to measure PFAS compounds in air.

Description:

A bench-scale three-furnace experimental system was built to simulate industrial processes of applying per- and polyfluoroalkyl substance (PFAS)-containing aqueous fluoropolymer dispersions to fibers and fabrics by thermally treating the coated material to affix the polymer. During this process, dispersion components, including fluorinated and non-fluorinated species, are vaporized and emitted as air emissions. Thermal processes necessary to sequentially dry, bake, and sinter the fluoropolymer are also suspected to cause chemical transformations within these air emissions. Initial experiments were performed with two commercially available dispersions and a model three-component mixture containing water, a common non-halogenated nonionic surfactant, and 0.3 wt% 6:2 fluorotelomer alcohol (6:2 FTOH). These were applied to fiberglass, and thermally processed at relevant temperatures and residence times. Vapor-phase emissions from the exits of each of the three sequential furnaces were sampled and characterized by several off-line and real-time mass spectrometry techniques for a limited set of targeted and non-targeted PFAS. Results indicate low, sub-part-per-billion by volume (ppbv), concentrations of several C1- and C2-chlorofluorocarbon and fluorocarbon species in experimental blanks. In addition, multiple PFAS thermal transformation products and multiple non-halogenated 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 (three-component) mixture. This suggests that temperatures typical of these industrial furnaces may also induce chemical transformations within the fluorinated air emissions. Additional experiments using two commercially available fluoropolymer dispersions indicate air emissions of part-per-million by volume (ppmv) concentrations of heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether (E1), as well as other PFAS at operationally relevant temperatures within different furnace zones. We suspect that E1 is a direct thermal decomposition product (via decarboxylation) of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoic acid (HFPO-DA) present in the dispersions as a surfactant, or as a residual polymer processing aid (PPA). 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.