Since fluorinated polymer coatings are used to impart durable oil-and-water-repellent properties on fabrics, potentially offering a persistent fiber characteristic for forensic fiber comparisons, the current study evaluated the persistence of these coatings by investigating the effects of outdoor weathering and laundering on detection and classification of the fluorinated oil-and-water-repellent coatings on 9 garments and 2 spray-coated fabric samples.
Single fibers from the samples were pyrolyzed and subjected to gas chromatography coupled to a fluorine-selective detector. The positive detection of coatings is indicated by a signal-to-noise ratio (S/N) >50 for the tallest peak in the pyrograms. Moreover, a multinomial logistic regression model trained using fibers prior to weathering and laundering was used to determine the class of the weathered and laundered fibers, providing a metric to evaluate the effect of these processes on fiber classification. Notably, fluorinated coatings were detected on all of the fibers exposed to outdoor elements in Arlington, VA, up to 12 weeks from August to October 2020, while a detection rate of 95.5 percent was achieved for samples laundered up to 10 wash cycles. The detection rate prior to weathering and laundering was 98 percent, indicating negligible effect of these processes on detection of coatings. The classification accuracy is determined to be 99 percent and 100 percent for weathered and laundered samples, respectively, illustrating that these processes do not significantly affect the major pyrolysis products of the coatings responsible for classification. These results highlight the persistence of the fluorinated oil-and-water-repellent fabric coatings and their potential for forensic fiber discrimination at single-fiber level. (publisher abstract modified)